Part of the work has been performed in the project JEMSiP_3D, which is funded by the Public Authorities in France, Germany, Hungary, The Netherlands, Norway and Sweden, as well as by the ENIAC Joint Undertaking. The authors would like to thank the Dimes Technology Centre staff for processing support.

Attention: S&#39;il vous plaît consulter toutes les fiches de données de sécurité des matériaux pertinents (FS) avant utilisation. Plusieurs des produits chimiques utilisés dans le processus de fabrication sont très toxiques et cancérigènes. Les nanomatériaux peuvent avoir des risques supplémentaires par rapport à leur homologue en vrac. S&#39;il vous plaît utiliser toutes les pratiques de sécurité appropriées lorsque vous travaillez avec des équipements, des produits chimiques ou des nanomatériaux, y compris l&#39;utilisation des contrôles d&#39;ingénierie (hottes) et les équipements de protection individuelle (lunettes de sécurité, gants, vêtements de salle blanche). 1. Alignement Marker Définition pour la lithographie <ol><li> Commencez avec qualité industrielle simple face polie Si (100) avec des tranches n ou de type p dopage. </li><li> Manteau de la tranche à 1,4 um de résine positive. Effectuez une hexaméthyldisilazane 90 sec (HMDS) de traitement à 130 ° C pour favoriser l&#39;adhérence de la résine, suivi par un refroidissement de la plaquette sur une plaque froide, spin-coating à la vitesse appropriée (3500 rpm), et un 90 sec cuisson douce unet 95 ° C. </li><li> L&#39;utilisation d&#39;un masque photo-lithographie et outil d&#39;exposition exposer les repères d&#39;alignement, la dose d&#39;exposition de 120 mJ / cm 2. </li><li> Effectuer un seul processus de développement flaque d&#39;eau. Effectuer un 90 sec 115 ° post-exposition de C cuire, puis 60 secondes en utilisant le développement de développeur et 90 sec dur cuire au four à 100 ° C pour durcir la résine. </li><li> Utilisation d&#39;un microscope pour examiner si les ouvertures dans la résine sont des dimensions correctes. </li><li> Etch 120 nm de Si en utilisant une gravure au plasma de chlore. Cette épaisseur donne un bon contraste pour les systèmes automatiques d&#39;alignement de l&#39;outil d&#39;exposition utilisée dans ce travail. Par exemple en utilisant un plasma à couplage inductif (ICP): 20/40 SCCM O 2 / CF 4, 5 mTorr, 60/500 W plateau / puissance RF ICP, 10 sec oxyde percée attaque, suivi par 80/40 SCCM Cl 2 / HBr , 60 mTorr, 20/500 W plateau / puissance RF ICP, 35 sec Si graver. </li><li> Utilisez un décapant de plasma d&#39;oxygène pour éliminer la résine photosensible (1 kW, 400 sccm O 2 avec endpodétection d&#39;int et 2 min surgravure). Comme la résine photosensible est durcie par le plasma normal solvant tel que l&#39;acétone ne peut pas être utilisé. </li><li> Nettoyer les plaquettes. Première les mettre pendant 10 min dans 99% de HNO 3, suivi d&#39;un rinçage à l&#39;eau DI jusqu&#39;à la résistivité de l&#39;eau est de 5 MQ (propre organique). Après ce nettoyage des plaquettes pendant 10 minutes à 65% de HNO 3 à 110 ° C, suivi d&#39;un rinçage à l&#39;eau déionisée jusqu&#39;à ce que la résistivité de l&#39;eau est 5 MQ (métal pur). Utilisez un sèche-rinceuse pour sécher les plaquettes. </li></ol> 2. fond métallique et diélectrique intercalaire dépôt <ol><li> Utilisation pulvérisation magnétron pour déposer la couche métallique inférieure par l&#39;intermédiaire de l&#39;essai. Un empilement de trois couches de métal doit être déposé: 500 nm de Ti, 50 nm de TiN, Ti et 100 nm. La première couche de Ti est de réduire la résistance de la pile, l&#39;étain est la couche de support pour la croissance réelle CNT, et la partie supérieure de Ti est de protéger le TiN de plasma contre les dommages lorsque la gravure de la couche 12 de SiO 2 </sup&gt;. Effectuer Ti pulvérisation cathodique en utilisant une cible de Ti pur avec Ar-plasma à une température de substrat de 350 ° C. Pour l&#39;étain pulvérisation réactive utiliser une combinaison de Ar et N 2, à nouveau à 350 ° C la température du substrat. </li><li> Utilisation de dépôt chimique en phase vapeur assisté par plasma (PECVD), le dépôt d&#39;une épaisse couche de SiO 2 à 1 um. Ici, l&#39;orthosilicate de tétraéthyle (TEOS) est utilisé comme précurseur à une température de cylindre de 350 ° C. <ol><li> Vérifiez l&#39;épaisseur de la couche de SiO 2 à l&#39;aide d&#39;un outil approprié, par exemple un réflectomètre ou ellipsomètre. </li></ol></li><li> Manteau de la tranche à 1,4 um de résine positive, en commençant par un traitement 90 sec HMDS à 130 ° C, suivi par un refroidissement de la plaquette sur une plaque froide, spin-coating à la vitesse appropriée (3500 rpm), et un 90 sec doux cuire au four à 95 ° C. </li><li> L&#39;utilisation d&#39;un masque photo-lithographie et outil d&#39;exposition, exposer le motif désiré d&#39;ouvertures, qui seront plus tard gravé dans le SiO 2 to former les vias, alignés sur les repères d&#39;alignement, la dose d&#39;exposition de 140 mJ / cm 2. </li><li> Effectuer un processus de développement de flaque d&#39;eau simple à partir d&#39;un 90 sec 115 ° post-exposition de C cuire, puis 60 secondes en utilisant le développement de développeur et 90 sec dur cuire au four à 100 ° C. </li><li> Utilisation d&#39;un microscope pour examiner si les ouvertures dans la résine sont des dimensions correctes et si la superposition des repères d&#39;alignement est correct. </li><li> Gravure plasma des ouvertures de contact dans le SiO 2. Par exemple, utiliser un graveur triode de plasma avec C 2 F 6 / CHF 3 36/144 sccm à 180 mTorr et 300 W de puissance RF. Si nécessaire, effectuer des tests de taux de gravure sur une pastille d&#39;essai, afin de minimiser au cours de la gravure de 5% à 10% du temps. Remarque: Bien que le Ti est résistant à la gravure réactive dans cette chimie du fluor, l&#39;exposition prolongée au plasma se traduira par gravure de la couche physique Ti. Si la couche de TiN est exposé au plasma cela aura un négatif influenCE sur la croissance de la CNT 12. Ne pas utiliser la gravure humide que cela se traduira par trop élargissement des ouvertures, ce qui rend la métallisation supérieure dans la partie 4 problématique. </li><li> Retirer la couche sacrificielle Ti par gravure humide dans 0,55% de HF pendant 60 secondes. Après gravure rincer les tranches avec de l&#39;eau DI jusqu&#39;à la résistivité de l&#39;eau est de 5 MQ et utiliser un sèche-rinceuse pour sécher les plaquettes. Remarque: En utilisant un microscope il peut être vérifié si la couche de Ti est gravée, la couche d&#39;étain aura une couleur brun-doré tandis que le Ti est gris métallisé. </li></ol> 3. Catalyst dépôt et CNT croissance <ol><li> Évaporer 5 nm de Co à l&#39;aide d&#39;un évaporateur à faisceau électronique. Pomper au moins jusqu&#39;à 2x10 -6 Torr, et chauffer les plaquettes à 60 ° C à l&#39;aide de lampes sous vide avant le dépôt de supprimer tout film d&#39;eau. La résine photosensible utilisée pour définir les ouvertures de contact est maintenu sur la plaquette de fournir des auto-alignement du catalyseur pour les ouvertures de contact dans le SiO 2. </li><li> RetirerCo en dehors des ouvertures de contact par lift-off. Pour le CO, il a été constaté que le tétrahydrofuranne (THF) donne les meilleurs résultats lift-off et de la croissance à basse température. N-méthyl-2-pyrrolidone (NMP), qui a été précédemment utilisé pour le décollage après l&#39;évaporation Fe, a été trouvé à des dommages une mesure de la Co trop tels à empêcher toute croissance CNT aligné. Mettez la plaque pendant 15 min dans un bain à ultrasons avec du THF à 35 ° C. Rincer à l&#39;eau DI pendant 5 min et sécher à l&#39;aide d&#39;une centrifugeuse ou de l&#39;azote pistolet. </li><li> Inspectez la plaquette sous un microscope et vérifier résister à résidus. Si les résidus restent effectuer un traitement plus ultrasons dans le THF, et éventuellement utiliser un chiffon doux spécial pour fins lift-off pour essuyer manuellement loin résidus. </li><li> Effectuer CNT croissance par dépôt chimique en phase vapeur basse pression (LPCVD). Utiliser la recette suivante: 8 min de pré-recuit à 350 ° C avec 700 sccm H 2 à 80 mbar, suivi d&#39;une croissance CNT par addition de 50 sccm C 2 H 2. A 350 ° C, 60min de la croissance donne environ 1 um de CNT. Le cas échéant effectuer un essai de croissance de régler la hauteur, qui doit être la même épaisseur que la couche de SiO 2. Refroidir le réacteur et purger utilisant N 2. </li><li> Utiliser un microscope électronique à balayage pour vérifier la hauteur de la CNT à l&#39;intérieur des ouvertures de moins de 45 ° d&#39;inclinaison, ou en préparant une section transversale. </li><li> Inspecter les échantillons en utilisant la spectroscopie Raman pour déterminer la cristallinité de la CNT 18. </li></ol> 4. Topside métallisation <ol><li> Utilisez pulvérisation magnétron pour déposer le métal dessus. Comme Ti est un bon métal pour contacter CNT 19, premier pulvérisation 100 nm de Ti, suivie de 2 um d&#39;Al (1% de Si) sans casser le vide. </li><li> Manteau de la tranche à 3,1 um de résine photosensible positive avec une viscosité plus élevée, à commencer par un traitement 90 sec HMDS à 130 ° C, suivi par un refroidissement de la plaquette sur une plaque froide, spin-coating à 3000 tpm, et une cuisson douce de 90 secondes à 95° C. </li><li> L&#39;utilisation d&#39;un masque photo-lithographie et outil d&#39;exposition exposer le motif métallique supérieure alignée sur les repères d&#39;alignement, la dose d&#39;exposition de 420 mJ / cm 2, l&#39;accent de -1. </li><li> Effectuer un seul processus de développement flaque d&#39;eau. Cela commence avec un 90 sec 115 ° post-exposition de C cuire, puis 60 secondes en utilisant le développement de développeur et 90 sec dur cuire au four à 100 ° C. </li><li> Utilisation d&#39;un microscope pour examiner si les lignes dans la réserve sont des dimensions correctes et si la superposition de marqueurs est correcte. </li><li> Etch la pile Ti / Al en utilisant la gravure par plasma de chlore. Par exemple en utilisant un plasma à couplage inductif: 30/40 SCCM Cl 2 / HBr, 5 mTorr, 40/500 W Puissance Platen / ICP RF avec détection de point final et de 80% en utilisant surgravure 15/30 SCCM Cl 2 / HBr. </li><li> Utilisez un décapant de plasma d&#39;oxygène pour éliminer la résine photosensible (1 kW, 400 sccm O 2 avec détection de point final et 2 min surgravure). Si la couverture métallique ne soit pas complète (à savoir, il y a des trous d&#39;épingle dans leCNT) utiliser un solvant organique (par exemple, NMP) pour enlever la résine photosensible afin de prévenir les dommages à plasma à la CNT. </li><li> Nettoyer les plaquettes. Les mettre pendant 10 minutes à 99% de HNO 3, suivi d&#39;un rinçage à l&#39;eau déionisée jusqu&#39;à ce que la résistivité de l&#39;eau est 5 MQ (en propre organique). Utilisez un sèche-rinceuse pour sécher les plaquettes. </li></ol> 5. Mesures <ol><li> Utiliser un microscope électronique à balayage selon les instructions du fabricant pour vérifier la métallisation haut de plaquettes. Note:. Si nécessaire, la plaquette peut être clivée mécaniquement afin de vérifier la CNT complète via l&#39;aide d&#39;un échantillon inclinaison de 90 °, résultant en des images comme le montre la Figure 3 Comme les échantillons sont électriquement conductrice aucune des étapes de traitement supplémentaires doivent être utilisés et les échantillons peuvent être montés directement dans la MEB. En général, les hautes tensions d&#39;accélération de 15 kV ou 20 peuvent être utilisés, mais si la couche de SiO 2 est en charge trop ce peut être réduite to 5 kV. </li><li> Effectuez 4 points mesures sonde IV en utilisant une station de la sonde en combinaison avec un semi-conducteur analyseur de paramètres tel que décrit dans la figure 1 et dans Vollebregt et al. 16. Remarque: Normalement, un balayage de tension de -0,5 à 0,5 V est suffisante, comme la chute de potentiel sur une interconnexion est idéalement petite. En utilisant une configuration de sonde à 4 points la résistance des aiguilles de sonde et les fils de résistances de la configuration de contacts sont omis. </li></ol>

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The authors have nothing to disclose.

Figure 1 affiche un aperçu schématique de la structure fabriquée dans ce travail, et qui a été utilisé pour les mesures de la sonde à 4 points. Comme le potentiel est mesuré par l&#39;intermédiaire des sondes portant pas de courant, la chute de potentiel exact (VH-L) sur le faisceau de CNT central et ses contacts avec le métal peut être mesurée. Plus grand diamètre faisceaux CNT sont utilisés pour communiquer avec la couche d&#39;étain fond des plots de contact, afin de réduir...

Le cuivre et le tungstène, les métaux qui sont actuellement utilisées pour les interconnexions à très grande échelle d&#39;intégration (VLSI) la technologie state-of-the-art, se rapprochent de leurs limites physiques en termes de fiabilité et de conductivité électrique 1. Bien que les transistors-mise à l&#39;échelle vers le bas améliore généralement leur performance, il augmente en fait la résistance et la densité de courant des interconnexions. Il en est résulté des interconnexions qui dominent la performance circuit intégré (IC) en termes de délai et de la consommation d&#39;énergie 2. Les nanotubes de carbone (CNT) ont été proposés comme alternative pour Cu et W métallisation, en particulier pour les interconnexions verticales (traversées) que CNT peuvent facilement été cultivées verticale 3. CNT a été démontré qu&#39;ils ont une excellente fiabilité électrique, ce qui permet un jusqu&#39;à 1000 fois plus élevée que la densité de courant Cu 4. En outre, la CNT ne souffrent pas de la surface et le grain diffusion de la frontière, ce qui augmente la resistivity de Cu à l&#39;échelle du nanomètre 5. Enfin, CNT se sont révélés être d&#39;excellents conducteurs thermiques 6, qui peuvent aider à la gestion thermique des puces VLSI à. Pour une intégration réussie de la CNT dans la technologie VLSI, il est important que les processus de croissance pour la CNT est faite compatible avec la fabrication de semiconducteurs. Cela nécessite la faible croissance de la température de la CNT (&lt;400 ° C) en utilisant des matériaux et des équipements qui sont considérées comme compatibles et évolutive pour la fabrication à grande échelle. Alors que de nombreux exemples de vias de test CNT ont été démontrés dans la littérature 7,8,9,10,11,12,13,14, la plupart d&#39;entre eux utilisent Fe comme catalyseur qui est considéré comme un contaminant dans la fabrication IC 15. En outre, la température de croissance utilisée dans un grand nombre de ces ouvrages est beaucoup plus élevé que la limite supérieure de 400 ° C. De préférence CNT devrait même être cultivé en dessous de 350 ° C, afin de permettre l&#39;intégration avec les diélectriques à faible kappa modernes ou souplesubstrats. Ici, nous présentons une méthode évolutive pour la croissance de CNT à des températures aussi basses que 350 ° C en utilisant comme catalyseur Co 16. Cette méthode est d&#39;intérêt pour la fabrication de différentes structures électriques constitués de alignés verticalement CNT dans les circuits intégrés, allant de l&#39;interconnexion et des électrodes de supercondensateurs et des dispositifs à émission de champ. Le métal du catalyseur Co est souvent utilisé dans la fabrication de circuits intégrés pour la fabrication de siliciure de 17, tandis que l&#39;étain est un matériau de barrière souvent utilisé 7. En outre, nous démontrons un procédé de fabrication de vias d&#39;essai CNT, tandis que seulement en utilisant des techniques de fabrication de semi-conducteur standard. Grâce à cela, des trous d&#39;interconnexion d&#39;essai CNT sont fabriqués, contrôlés par microscopie électronique à balayage (SEM) et spectroscopie Raman, et caractérisé électriquement.

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			<td style="width:291px;">Comments/Description</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:307px;">Si (100) wafer 4&#34;</td>
			<td style="width:188px;">International Wafer Service</td>
			<td style="width:119px;"></td>
			<td>Resisitivity: 2-5 m&#937;-cm, thickness: 525 &#181;m&#160;</td>
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			<td height="21" style="height:21px;width:307px;">Ti-sputtertarget (99.995 % purity)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:307px;">Al (1% Si)-sputtertarget (99.999 % purity)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="21" style="height:21px;width:307px;">Co (99.95 % purity)</td>
			<td style="width:188px;">Kurt J. Lesker</td>
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			<td height="21" style="height:21px;width:307px;">SPR3012 positive photoresist</td>
			<td style="width:188px;">Dow Electronic Materials</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:307px;">MF-322 developer</td>
			<td style="width:188px;">Dow Electronic Materials</td>
			<td style="width:119px;"></td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:307px;">HNO3 (99.9 %)</td>
			<td style="width:188px;">KMG Ultra Pure Chemicals</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="21" style="height:21px;width:307px;">HNO3 (69.5%)</td>
			<td style="width:188px;">KMG Ultra Pure Chemicals</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="21" style="height:21px;width:307px;">HF 0.55%</td>
			<td style="width:188px;">Honeywell</td>
			<td style="width:119px;"></td>
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			<td height="21" style="height:21px;width:307px;">Tetrahydrofuran</td>
			<td style="width:188px;">JT Baker</td>
			<td style="width:119px;"></td>
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			<td height="21" style="height:21px;width:307px;">Acetone</td>
			<td style="width:188px;">Sigma-Aldrich</td>
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			<td height="21" style="height:21px;width:307px;">ECI3027 positive photoresist</td>
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			<td height="21" style="height:21px;width:307px;">Tetraethyl orthosilicate (TEOS)</td>
			<td style="width:188px;">Praxair</td>
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			<td style="width:188px;">Company</td>
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			<td>Comments/Description</td>
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			<td height="21" style="height:21px;width:307px;">N2 (99.9990%)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:307px;">O2 (99.9999%)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:307px;">CF4 (99.9970%)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:307px;">CL2 (99.9900%)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="21" style="height:21px;width:307px;">HBr (99.9950%)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="21" style="height:21px;width:307px;">Ar (99.9990%)</td>
			<td style="width:188px;">Praxair</td>
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			<td height="21" style="height:21px;width:307px;">C2F6 (99.9990%)</td>
			<td style="width:188px;">Praxair</td>
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			<td height="21" style="height:21px;width:307px;">CHF3 (99.9950%)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="21" style="height:21px;width:307px;">H2 (99.9950%)</td>
			<td style="width:188px;">Praxair</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="21" style="height:21px;width:307px;">C2H2 (99.6000%)</td>
			<td style="width:188px;">Praxair</td>
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			<td height="21" style="height:21px;width:307px;">ASML PAS5500/80 waferstepper</td>
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			<td height="21" style="height:21px;width:307px;">SPTS &#937;mega 201 plasma etcher</td>
			<td style="width:188px;">SPTS</td>
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			<td>Used for Si and metal etching</td>
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			<td style="width:188px;">SPTS</td>
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			<td height="21" style="height:21px;width:307px;">Novellus Concept One PECVD</td>
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			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:307px;">Drytek 384T plasma etcher</td>
			<td style="width:188px;">LAM</td>
			<td style="width:119px;"></td>
			<td>Used for oxide etching</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:307px;">CHA Solution e-beam evaporator</td>
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			<td height="21" style="height:21px;width:307px;">AIXTRON BlackMagic Pro CVD tool</td>
			<td style="width:188px;">AIXTRON</td>
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			<td>Carbon nanotube growth</td>
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			<td height="21" style="height:21px;width:307px;">Tepla 300</td>
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			<td height="21" style="height:21px;width:307px;">Leitz MPV-SP reflecometer</td>
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			<td style="width:188px;">Cascade Microtech</td>
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fabrication of low temperature carbon nanotube vertical interconnects compatible with semiconductor technology

We demonstrate a method for the low temperature growth (350 &#176;C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive thin-films. Due to the low growth temperature, the process allows integration with modern low-&#954; dielectrics and some flexible substrates. The process is compatible with standard semiconductor fabrication, and a method for the fabrication of electrical 4-point probe test structures for vertical interconnect test structures is presented. Using scanning electron microscopy the morphology of the CNT bundles is investigated, which demonstrates vertical alignment of the CNT and can be used to tune the CNT growth time. With Raman spectroscopy the crystallinity of the CNT is investigated. It was found that the CNT have many defects, due to the low growth temperature. The electrical current-voltage measurements of the test vertical interconnects displays a linear response, indicating good ohmic contact was achieved between the CNT bundle and the top and bottom metal electrodes. The obtained resistivities of the CNT bundle are among the average values in the literature, while a record-low CNT growth temperature was used.

La conception de la structure de mesure utilisée dans ce travail peut être trouvé dans la figure 1. En utilisant une telle structure de la mesure de la résistance de faisceau CNT et les résistances de contact métal-CNT peut être déterminée avec précision, comme sonde et fils résistances sont contournées. La résistance du faisceau est une mesure pour la qualité et la densité du faisceau CNT. Afin de déterminer les faisceaux de résistance de contact de différentes longue...

Watch this Scientific Journal Video about Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology at JoVE.com

Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology

A method for the growth of low temperature vertically-aligned carbon nanotubes, and the subsequent fabrication of vertical interconnect electrical test structures using semiconductor fabrication is presented.

Fabrication de basse température de nanotubes de carbone interconnexions verticales Compatible avec la technologie des semiconducteurs

We demonstrate a method for the low temperature growth (350 &#176;C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive ...

fabrication-low-temperature-carbon-nanotube-vertical-interconnects

Research

JoVE Journal

Engineering

7.6K vues.  Delft University of Technology. A method for the growth of low temperature vertically-aligned carbon nanotubes, and the subsequent fabrication of vertical interconnect electrical test structures using semiconductor fabrication is presented.

Vidéo: Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology

Fabrication, Densification, and Replica Molding of 3D Carbon Nanotube Microstructures

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip devices, and their applications. In particular, capabilities for cost-effective fabrication of polymer microstructures were transformed by the advent of soft lithography and other micromolding techniques 1, 2, and this led a revolution in applications of microfabrication to biomedical engineering and biology. Nevertheless, it remains challenging to fabricate microstructures with well-defined nanoscale surface textures, and to fabricate arbitrary 3D shapes at the micro-scale. Robustness of master molds and maintenance of shape integrity is especially important to achieve high fidelity replication of complex structures and preserving their nanoscale surface texture. The combination of hierarchical textures, and heterogeneous shapes, is a profound challenge to existing microfabrication methods that largely rely upon top-down etching using fixed mask templates. On the other hand, the bottom-up synthesis of nanostructures such as nanotubes and nanowires can offer new capabilities to microfabrication, in particular by taking advantage of the collective self-organization of nanostructures, and local control of their growth behavior with respect to microfabricated patterns. 
Our goal is to introduce vertically aligned carbon nanotubes (CNTs), which we refer to as CNT "forests", as a new microfabrication material. We present details of a suite of related methods recently developed by our group: fabrication of CNT forest microstructures by thermal CVD from lithographically patterned catalyst thin films; self-directed elastocapillary densification of CNT microstructures; and replica molding of polymer microstructures using CNT composite master molds. In particular, our work shows that self-directed capillary densification ("capillary forming"), which is performed by condensation of a solvent onto the substrate with CNT microstructures, significantly increases the packing density of CNTs. This process enables directed transformation of vertical CNT microstructures into straight, inclined, and twisted shapes, which have robust mechanical properties exceeding those of typical microfabrication polymers. This in turn enables formation of nanocomposite CNT master molds by capillary-driven infiltration of polymers. The replica structures exhibit the anisotropic nanoscale texture of the aligned CNTs, and can have walls with sub-micron thickness and aspect ratios exceeding 50:1. Integration of CNT microstructures in fabrication offers further opportunity to exploit the electrical and thermal properties of CNTs, and diverse capabilities for chemical and biochemical functionalization 3.

We present methods for fabrication of patterned microstructures of vertically aligned carbon nanotubes (CNTs), and their use as master molds for production of polymer microstructures with organized nanoscale surface texture. The CNT forests are densified by condensation of solvent onto the substrate, which significantly increases their packing density and enables self-directed formation of 3D shapes.

Moulage de fabrication, de densification, et une réplique de 3D Microstructures de nanotubes de carbone

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip ...

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Ingénierie

Dry Oxidation and Vacuum Annealing Treatments for Tuning the Wetting Properties of Carbon Nanotube Arrays

In this article, we describe a simple method to reversibly tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays. Here, CNT arrays are defined as densely packed multi-walled carbon nanotubes oriented perpendicular to the growth substrate as a result of a growth process by the standard thermal chemical vapor deposition (CVD) technique.1,2 These CNT arrays are then exposed to vacuum annealing treatment to make them more hydrophobic or to dry oxidation treatment to render them more hydrophilic. The hydrophobic CNT arrays can be turned hydrophilic by exposing them to dry oxidation treatment, while the hydrophilic CNT arrays can be turned hydrophobic by exposing them to vacuum annealing treatment. Using a combination of both treatments, CNT arrays can be repeatedly switched between hydrophilic and hydrophobic.2 Therefore, such combination show a very high potential in many industrial and consumer applications, including drug delivery system and high power density supercapacitors.3-5
The key to vary the wettability of CNT arrays is to control the surface concentration of oxygen adsorbates. Basically oxygen adsorbates can be introduced by exposing the CNT arrays to any oxidation treatment. Here we use dry oxidation treatments, such as oxygen plasma and UV/ozone, to functionalize the surface of CNT with oxygenated functional groups. These oxygenated functional groups allow hydrogen bond between the surface of CNT and water molecules to form, rendering the CNT hydrophilic. To turn them hydrophobic, adsorbed oxygen must be removed from the surface of CNT. Here we employ vacuum annealing treatment to induce oxygen desorption process. CNT arrays with extremely low surface concentration of oxygen adsorbates exhibit a superhydrophobic behavior.

This article describes a simple method to fabricate vertically aligned carbon nanotube arrays by CVD and to subsequently tune their wetting properties by exposing them to vacuum annealing or dry oxidation treatment.

L&#39;oxydation à sec et un recuit sous vide Traitements pour Réglage des propriétés de mouillage de tableaux de nanotubes de carbone

In this article, we describe a simple method to reversibly  tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays.  Here, CNT ...

Synthesis and Functionalization of Nitrogen-doped Carbon Nanotube Cups with Gold Nanoparticles as Cork Stoppers

Nitrogen-doped carbon nanotubes consist of many cup-shaped graphitic compartments termed as nitrogen-doped carbon nanotube cups (NCNCs). These as-synthesized graphitic nanocups from chemical vapor deposition (CVD) method were stacked in a head-to-tail fashion held only through noncovalent interactions. Individual NCNCs can be isolated out of their stacking structure through a series of chemical and physical separation processes. First, as-synthesized NCNCs were oxidized in a mixture of strong acids to introduce oxygen-containing defects on the graphitic walls. The oxidized NCNCs were then processed using high-intensity probe-tip sonication which effectively separated the stacked NCNCs into individual graphitic nanocups. Owing to their abundant oxygen and nitrogen surface functionalities, the resulted individual NCNCs are highly hydrophilic and can be effectively functionalized with gold nanoparticles (GNPs), which preferentially fit in the opening of the cups as cork stoppers. These graphitic nanocups corked with GNPs may find promising applications as nanoscale containers and drug carriers.

We discussed the synthesis of individual graphitic nanocups using a series of techniques including chemical vapor deposition, acid oxidation and probe-tip sonication. By citrate reduction of HAuCl4, the graphitic nanocups were effectively corked with gold nanoparticles due to the chemically reactive edges of the cups.

Synthèse et fonctionnalisation des dopé à l&#39;azote Coupes de nanotubes de carbone avec des nanoparticules d&#39;or que les bouchons de liège

Nitrogen-doped carbon  nanotubes consist of many cup-shaped graphitic compartments termed as  nitrogen-doped carbon nanotube cups (NCNCs).  These ...

Writing and Low-Temperature Characterization of Oxide Nanostructures

Oxide nanoelectronics is a rapidly growing field which seeks to develop novel materials with multifunctional behavior at nanoscale dimensions. Oxide interfaces exhibit a wide range of properties that can be controlled include conduction, piezoelectric behavior, ferromagnetism, superconductivity and nonlinear optical properties. Recently, methods for controlling these properties at extreme nanoscale dimensions have been discovered and developed. Here are described explicit step-by-step procedures for creating LaAlO3/SrTiO3 nanostructures using a reversible conductive atomic force microscopy technique. The processing steps for creating electrical contacts to the LaAlO3/SrTiO3 interface are first described. Conductive nanostructures are created by applying voltages to a conductive atomic force microscope tip and locally switching the LaAlO3/SrTiO3 interface to a conductive state. A versatile nanolithography toolkit has been developed expressly for the purpose of controlling the atomic force microscope (AFM) tip path and voltage. Then, these nanostructures are placed in a cryostat and transport measurements are performed. The procedures described here should be useful to others wishing to conduct research in oxide nanoelectronics.

Oxide nanostructures provide new opportunities for science and technology. The interfacial conductivity between LaAlO3 and SrTiO3 can be controlled with near-atomic precision using a conductive atomic force microscopy technique. The protocol for creating and measuring conductive nanostructures at LaAlO3/SrTiO3 interfaces is demonstrated.

Écrit et à basse température Caractérisation des nanostructures d&#39;oxyde

Oxide nanoelectronics is a rapidly growing field which seeks to develop novel materials with multifunctional behavior at nanoscale dimensions.  Oxide ...

Ohmic Contact Fabrication Using a Focused-ion Beam Technique and Electrical Characterization for Layer Semiconductor Nanostructures

Layer semiconductors with easily processed two-dimensional (2D) structures exhibit indirect-to-direct bandgap transitions and superior transistor performance, which suggest a new direction for the development of next-generation ultrathin and flexible photonic and electronic devices. Enhanced luminescence quantum efficiency has been widely observed in these atomically thin 2D crystals. However, dimension effects beyond quantum confinement thicknesses or even at the micrometer scale are not expected and have rarely been observed. In this study, molybdenum diselenide (MoSe2) layer crystals with a thickness range of 6-2,700 nm were fabricated as two- or four-terminal devices. Ohmic contact formation was successfully achieved by the focused-ion beam (FIB) deposition method using platinum (Pt) as a contact metal. Layer crystals with various thicknesses were prepared through simple mechanical exfoliation by using dicing tape. Current-voltage curve measurements were performed to determine the conductivity value of the layer nanocrystals. In addition, high-resolution transmission electron microscopy, selected-area electron diffractometry, and energy-dispersive X-ray spectroscopy were used to characterize the interface of the metal&#8211;semiconductor contact of the FIB-fabricated MoSe2 devices. After applying the approaches, the substantial thickness-dependent electrical conductivity in a wide thickness range for the MoSe2-layer semiconductor was observed. The conductivity increased by over two orders of magnitude from 4.6 to 1,500 &#937;&#8722;1 cm&#8722;1, with a decrease in the thickness from 2,700 to 6 nm. In addition, the temperature-dependent conductivity indicated that the thin MoSe2 multilayers exhibited considerably weak semiconducting behavior with activation energies of 3.5-8.5 meV, which are considerably smaller than those (36-38 meV) of the bulk. Probable surface-dominant transport properties and the presence of a high surface electron concentration in MoSe2 are proposed. Similar results can be obtained for other layer semiconductor materials such as MoS2 and WS2.

We describe the approaches for the device fabrication and electrical characterization of molybdenum diselenide (MoSe2) layer semiconductor nanostructures with different thicknesses. In addition, the fabrication of ohmic contacts for MoSe2-layer nanocrystals by the focused-ion beam deposition method using platinum (Pt) as a contact metal is described.

Contact ohmique fabrication utilisant une technique Focused Ion Beam-et caractérisation électrique pour la couche semi-conducteurs Nanostructures

Layer semiconductors with easily processed two-dimensional (2D) structures exhibit indirect-to-direct bandgap transitions and superior transistor ...

Advanced Experimental Methods for Low-temperature Magnetotransport Measurement of Novel Materials

Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film synthesis) for the purpose of exploratory materials research. Certain materials pose a challenge wherein the traditional bulk Hall bar device fabrication method is insufficient to produce a measureable device for sample transport measurement, principally because the single crystal size is too small to attach wire leads to the sample in a Hall bar configuration. This can be, for example, because the first batch of a new material synthesized yields very small single crystals or because flakes of samples of one to very few monolayers are desired. In order to enable rapid characterization of materials that may be carried out in parallel with improvements to their growth methodology, a method of device fabrication for very small samples has been devised to permit the characterization of novel materials as soon as a preliminary batch has been produced. A slight variation of this methodology is applicable to producing devices using exfoliated samples of two-dimensional materials such as graphene, hexagonal boron nitride (hBN), and transition metal dichalcogenides (TMDs), as well as multilayer heterostructures of such materials. Here we present detailed protocols for the experimental device fabrication of fragments and flakes of novel materials with micron-sized dimensions onto substrate and subsequent measurement in a commercial superconducting magnet, dry helium close-cycle cryostat magnetotransport system at temperatures down to 0.300 K and magnetic fields up to 12 T.

We describe the methodology of mechanical exfoliation and deposition of flakes of novel materials with micron-sized dimensions onto substrate, fabrication of experimental device structures for transport experimentation, and the magnetotransport measurement in a dry helium close-cycle cryostat at temperatures down to 0.300 K and magnetic fields up to 12 T.

Méthodes expérimentales avancées pour basse température magnétotransport mesure de nouveaux matériaux

Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film ...

Precision Milling of Carbon Nanotube Forests Using Low Pressure Scanning Electron Microscopy

A nanoscale fabrication technique appropriate for milling carbon nanotube (CNT) forests is described. The technique utilizes an environmental scanning electron microscope (ESEM) operating with a low pressure water vapor ambient. In this technique, a portion of the electron beam interacts with the water vapor in the vicinity of the CNT sample, dissociating the water molecules into hydroxyl radicals and other species by radiolysis. The remainder of the electron beam interacts with the CNT forest sample, making it susceptible to oxidation from the chemical products of radiolysis. This technique may be used to trim a selected region of an individual CNT, or it may be used to remove hundreds of cubic microns of material by adjusting ESEM parameters. The machining resolution is similar to the imaging resolution of the ESEM itself. The technique produces only small quantities of carbon residue along the boundaries of the cutting zone, with minimal effect on the native structural morphology of the CNT forest.

Low pressure scanning electron microscopy in a water vapor ambient is used to machine nanoscale to microscale features in carbon nanotube forests.

Fraisage de précision des nanotubes de carbone des forêts Utilisation Numérisation basse pression Electron Microscopy

A nanoscale fabrication technique appropriate for milling carbon nanotube (CNT) forests is described. The technique utilizes an environmental scanning ...

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia (YSZ) Scaffolds by In Situ Carbon Templating Xerogels

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) scaffolds with tunable specific surface areas up to 80 m2&#183;g-1. An aqueous solution of a zirconium salt, yttrium salt, and glucose is mixed with propylene oxide (PO) to form a gel. The gel is dried under ambient conditions to form a xerogel. The xerogel is pressed into pellets and then sintered in an argon atmosphere. During sintering, a YSZ ceramic phase forms and the organic components decompose, leaving behind amorphous carbon. The carbon formed in situ serves as a hard template, preserving a high surface area YSZ nanomorphology at sintering temperature. The carbon is subsequently removed by oxidation in air at low temperature, resulting in a porous, nanostructured YSZ scaffold. The concentration of the carbon template and the final scaffold surface area can be systematically tuned by varying the glucose concentration in the gel synthesis. The carbon template concentration was quantified using thermogravimetric analysis (TGA), the surface area and pore size distribution was determined by physical adsorption measurements, and the morphology was characterized using scanning electron microscopy (SEM). Phase purity and crystallite size was determined using X-ray diffraction (XRD). This fabrication approach provides a novel, flexible platform for realizing unprecedented scaffold surface areas and nanomorphologies for ceramic-based electrochemical energy conversion applications, e.g. solid oxide fuel cell (SOFC) electrodes.

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia YSZ Scaffolds by In Situ Carbon Templating Xerogels

A protocol for fabricating porous, nanostructured yttria-stabilized-zirconia (YSZ) scaffolds at temperatures between 1,000 &#176;C and 1,400 &#176;C is presented.

Fabrication à haute température de nanostructurés yttriée-Zircon (YSZ) par scellants<em&gt; In Situ</em&gt; Carbon Templating xérogels

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) ...

Fabrication of 3D Carbon Microelectromechanical Systems (C-MEMS)

A wide range of carbon sources are available in nature, with a variety of micro-/nanostructure configurations. Here, a novel technique to fabricate long and hollow glassy carbon microfibers derived from human hairs is introduced. The long and hollow carbon structures were made by the pyrolysis of human hair at 900 &#176;C in a N2 atmosphere. The morphology and chemical composition of natural and pyrolyzed human hairs were investigated using scanning electron microscopy (SEM) and electron-dispersive X-ray spectroscopy (EDX), respectively, to estimate the physical and chemical changes due to pyrolysis. Raman spectroscopy was used to confirm the glassy nature of the carbon microstructures. Pyrolyzed hair carbon was introduced to modify screen-printed carbon electrodes ; the modified electrodes were then applied to the electrochemical sensing of dopamine and ascorbic acid. Sensing performance of the modified sensors was improved as compared to the unmodified sensors. To obtain the desired carbon structure design, carbon micro-/nanoelectromechanical system (C-MEMS/C-NEMS) technology was developed. The most common C-MEMS/C-NEMS fabrication process consists of two steps: (i) the patterning of a carbon-rich base material, such as a photosensitive polymer, using photolithography; and (ii) carbonization through the pyrolysis of the patterned polymer in an oxygen-free environment. The C-MEMS/NEMS process has been widely used to develop microelectronic devices for various applications, including in micro-batteries, supercapacitors, glucose sensors, gas sensors, fuel cells, and triboelectric nanogenerators. Here, recent developments of a high-aspect ratio solid and hollow carbon microstructures with SU8 photoresists are discussed. The structural shrinkage during pyrolysis was investigated using confocal microscopy and SEM. Raman spectroscopy was used to confirm the crystallinity of the structure, and the atomic percentage of the elements present in the material before and after pyrolysis was measured using EDX.

Fabrication of 3D Carbon Microelectromechanical Systems C-MEMS

Long and hollow glassy carbon microfibers were fabricated based on the pyrolysis of a natural product, human hair. The two fabrication steps of carbon microelectromechanical and carbon nanoelectromechanical systems, or C-MEMS and C-NEMS, are: (i) photolithography of a carbon-rich polymer precursor and (ii) pyrolysis of the patterned polymer precursor.

Fabrication de systèmes microélectromécaniques en carbone 3D (C-MEMS)

A wide range of carbon sources are available in nature, with a variety of micro-/nanostructure configurations. Here, a novel technique to fabricate long ...

Flow-assisted Dielectrophoresis: A Low Cost Method for the Fabrication of High Performance Solution-processable Nanowire Devices

Flow-assisted dielectrophoresis (DEP) is an efficient self-assembly method for the controllable and reproducible positioning, alignment, and selection of nanowires. DEP is used for nanowire analysis, characterization, and for solution-based fabrication of semiconducting devices. The method works by applying an alternating electric field between metallic electrodes. The nanowire formulation is then dropped onto the electrodes which are on an inclined surface to create a flow of the formulation using gravity. The nanowires then align along the gradient of the electric field and in the direction of the liquid flow. The frequency of the field can be adjusted to select nanowires with superior conductivity and lower trap density. 
In this work, flow-assisted DEP is used to create nanowire field effect transistors. Flow-assisted DEP has several advantages: it allows selection of nanowire electrical properties; control of nanowire length; placement of nanowires in specific areas; control of orientation of nanowires; and control of nanowire density in the device. 
The technique can be expanded to many other applications such as gas sensors and microwave switches. The technique is efficient, quick, reproducible, and it uses a minimal amount of dilute solution making it ideal for the testing of novel nanomaterials. Wafer scale assembly of nanowire devices can also be achieved using this technique, allowing large numbers of samples for testing and large-area electronic applications.

In this paper, flow assisted dielectrophoresis is demonstrated for the self-assembly of nanowire devices. The fabrication of a silicon nanowire field effect transistor is shown as an example.

Flux-aidé diélectrophorèse : Une méthode Low Cost pour la Fabrication des dispositifs de nanofils traitable-Solution Haute Performance

Flow-assisted dielectrophoresis (DEP) is an efficient self-assembly method for the controllable and reproducible positioning, alignment, and selection of ...