This work was performed in part at the Micro Nano Research Facility at RMIT University in the Victorian Node of the Australian National Fabrication Facility (ANFF). The authors acknowledge the facilities, and the scientific and technical assistance of the RMIT University&#39;s Microscopy, Microanalysis Facility, a linked laboratory of the Microscopy Australia. Scholarship support from the Australian Postgraduate Award (APA)/Research Training Program (RTP) scheme of the Australian government is acknowledged. We thank Professor Madhu Bhaskaran, Associate Professor Sumeet Walia, Dr. Matthew Field, and Mr. Brenton Cook for their guidance and helpful discussions.

1. Fabrication process and electrical characterization
<ol>
	<li>Use standard image reversal photolithography9 to pattern bottom electrode (BE layer 1) with photoresist&#160;of the devices using the following parameters:
	<ol>
		<li>Spin coat the photoresist at 3,000&#160;rpm, soft bake it at 90 &#176;C for 60&#160;s, expose with 25&#160;mJ/cm2 with a 405&#160;nm laser, bake at 120 &#176;C for 120&#160;s, perform flood exposure with 21 mW/cm2 and a 400&#160;nm laser, develop using developer, and rinse with deionized water.</li>
	</ol>
	</li>
	<li>Deposit 5&#160;nm titanium (Ti) for adhesion and 15&#160;nm of platinum (Pt) on top with an electron beam evaporator system with&#160;the substrate patterned on layer 1.</li>
	<li>Lift-off the deposited metals by placing the substrate in an acetone bath for ~20&#160;mins. Then, apply ultrasonic vibrations for 2&#160;min, and rinse with acetone and isopropyl alcohol (IPA) to complete the BE patterns. Repeat if the lift-off is not clean (Figure 1A, step 1).</li>
	<li>Pattern the functional oxide layer (layer 2) with photolithography on top of the BE as described in step 1.1.</li>
	<li>Deposit ~100&#160;nm of a-VOx and 5&#160;nm of Ti on top of layer 2 using a sputtering system10.</li>
	<li>Lift-off the functional oxide by placing the substrate in an acetone bath and applying pulsed ultrasonic vibrations manually with 2&#8211;3&#160;s pulses to finalize the functional oxide patterns. Repeat the procedure if the patterns are not clean. (Figure 1A, step 2 and step 3)</li>
	<li>Similarly, complete the top electrode (TE) (layer 3) patterns with Ti_20&#160;nm/Pt_200&#160;nm using image reversal photolithography, electron beam evaporation, and the lift-off process described in step&#160;1.&#160;(Figure 1A, step 4) 
	NOTE: This completes the fabrication of the cross-point device, Figure 1B.</li>
	<li>Perform electrical and temperature analysis on the fabricated device to understand its resistance switching performance.
	<ol>
		<li>Use the source meter with two-probe direct current (DC) I&#8211;V measurement system and a probe station for electrical measurements.</li>
		<li>Always maintain the relevant current compliance to avoid damaging the devices.</li>
		<li>To analyze the device&#39;s current behavior, perform voltage-controlled analysis and apply voltage sweeps starting with a low voltage of 0.1&#160;V in positive bias and increasing slowly until electroforming is observed. 
		NOTE: Electroforming is a one-time event at which a few nanometer-wide conductive filaments are formed within the initially insulating functional oxide at a particular voltage, which depends on intrinsic material properties and device dimensions. At this point, a sudden drop in resistance or increase in current is observed on the current-voltage graph due to a formed conductive path.</li>
		<li>After electroforming, apply bidirectional voltage sweeps to achieve volatile threshold switching performance. Adjust the voltage to achieve a high ON/OFF ratio. In this case, a switching ratio of ~10 was attained.</li>
		<li>Analyze the current-voltage characteristics at different temperatures from room temperature to 90 &#176;C increasing in 10&#160;&#176;C steps and reverse back to room temperature using a temperature-controlled stage.</li>
	</ol>
	</li>
</ol>
2. Gridbar and biasing chip mounting
<ol>
	<li>Design the FIB optimized gridbar in CAD software and manufacture using standard machining techniques in-house for mounting the biasing/heating chips used for in&#160;situ TEM experiments, as shown in Figure 2. 
	NOTE: Figure 2A shows separate parts of the gridbar to mount three chips simultaneously in the square shaped trenches. Figure 2B shows the zoomed squared trench section designed to fit the commercially available in&#160;situ biasing/heating chips for TEM.</li>
	<li>Clean the biasing chip by placing it in a glass Petri dish filled with acetone and gently rotate for 2 min. Then remove the chip and place it in a Petri dish filled with methanol and gently rotate for 2 min. Finally, blow dry with low pressured nitrogen. 
	NOTE: Commercially bought biasing chips, referred to as E-chips, have a photoresist coating for protection.</li>
	<li>Align the precleaned biasing chip in square trenches of gridbar, as seen in Figure 2C.</li>
	<li>Fix the grid cover on top of the biasing chip with screws to finalize the placement of the E-chip on the gridbar (Figure 2D).</li>
</ol>
3. Lamella preparation, mounting on biasing chip using focused ion beam, and in&#160;situ transmission electron microscopy
<ol>
	<li>Fabricate the samples separately as described in section 1 with a thicker BE of Ti_10&#160;nm/Pt_100&#160;nm, as seen in Figure 3A.</li>
	<li>Mount the newly prepared sample on a metal stub using conductive carbon tape and load in the FIB chamber. Apply additional tape on the sample for grounding to avoid charging problems.</li>
	<li>Load the biasing chip-mounted gridbar in the chamber at a 52&#176; tilt (see Figure 3B). This will be either perpendicular or parallel to the ion beam column depending on the stage rotation.</li>
	<li>Focus, astigmate, and align the electron beam on a sample surface using the microscope physical control panel and software on lamella preparation locations.</li>
	<li>Check the eucentric height of the focused sample location and beam coincidence for the electron beam and ion beam. 
	NOTE: The eucentric height is the position where the sample&#8217;s image does not move when the sample is tilted.</li>
	<li>Click on Auto TEM program (automatic lamella preparation program) to run it on the focused sample location using the microscope control software. The automatic program follows the sequence described below. 
	NOTE: This will complete the process for creating a TEM lamella (Figure 4). The progress of the AutoTEM program can be observed live on the desktop screen.
	<ol>
		<li>Create cross fiducial alignment markers with silicon&#160;milling and deposit a 1.5&#160;&#181;m-thick carbon protective layer over the 20 &#181;m x 5&#160;&#181;m area between alignment markers.</li>
		<li>Mill trenches on either side of carbon protective layer with a 5&#160;nA ion beam current to create the lamella.</li>
		<li>Thin the lamella with a 1&#160;nA ion beam current first and then with 300&#160;pA ion beam current to reach a 1&#160;&#181;m thickness.</li>
	</ol>
	</li>
	<li>Tilt the sample to 7&#176; to perform a J-cut on the lamella for separation from the substrate.</li>
	<li>Tilt the sample to 0&#176; (i.e., perpendicular to the electron beam column) and attach the lamella to the manipulator needle by wielding using Pt (Figure 5A).</li>
	<li>After attachment to the micromanipulator, separate the lamella from the substrate with the final cut and slowly retract the micromanipulator (Figure 5B).</li>
	<li>Focus the beam on the top edge of biasing chip on the gridbar, the lamella mounting position.</li>
	<li>Bring the lamella slowly towards the biasing chip with the manipulator needle (Figure 6A).</li>
	<li>Align the lamella in the center of the 17&#160;&#181;m gap on the top edge of the biasing chip. Slowly move it down until it barely touches the chip surface and weld the bottom edges of the lamella to the chip using Pt (Figure 6B).</li>
	<li>Cut the micromanipulator free from the lamella with silicon milling and retract the micromanipulator.</li>
	<li>Connect the top edges of the lamella with Pt traces to the two electrodes of the biasing chip for electrical connections (Figure 6C). 
	NOTE: The TE and BE are shorted at this point on both left and right sides.</li>
	<li>Thin the center region of lamella first using 300&#160;pA, and then with 100&#160;pA ion beams to make the lamella less than 100&#160;nm thick (Figure 6D) by tilting the specimen front and back by 2&#176; to ensure parallel faces and a uniform thickness.</li>
	<li>Polish out the ion beam-damaged layer with the Ga beam accelerating voltage of 5&#160;kV at an angle of 5&#176; to the surface on both faces.</li>
	<li>Remove the short connection between the top and bottom electrodes of the device with isolation cuts in the thinned region to create a current path from BE to TE through the active region (Figure 7A).</li>
	<li>Mount the biasing chip with lamella on the biasing chip holder and then load the biasing chip holder into the TEM chamber.</li>
	<li>Connect the wires from the biasing chip holder to the source meter and a control PC. 
	NOTE: Carefully place the connection wires to relieve the strain and minimize any vibrations during the experiment.</li>
	<li>Wait for the TEM chamber pressure to drop to 4e-5&#160;Torr and then focus, astigmate, and align the electron beam on a cross section of the lamella surface using the TEM control knobs.</li>
	<li>Apply voltage sweeps or constant voltage at different biasing voltages and collect the TEM micrographs in situ. 
	NOTE: Data related to diffraction patterns, electron diffraction X-ray spectroscopy (EDX), and electron energy loss spectroscopy (EELS) mapping can also be collected at different biasing voltages in situ.</li>
</ol>

<ol>
	<li>Kozma, R., Pino, R. E., Pazienza, G. E., Kozma, R., Pino, R. E., Pazienza, G. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Advances in Neuromorphic Memristor Science and Applications. , 9-14 (2012).</li><li>Pan, F., Gao, S., Chen, C., Song, C., Zeng, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recent+progress+in+resistive+random+access+memories:+Materials,+switching+mechanisms,+and+performance.">Recent progress in resistive random access memories: Materials, switching mechanisms, and performance.</a> Materials Science and Engineering: R: Reports. 83, 1-59 (2014).</li><li>Zhou, Y., Ramanathan, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mott+Memory+and+Neuromorphic+Devices.">Mott Memory and Neuromorphic Devices.</a> Proceedings of the IEEE. 103 (8), 1289-1310 (2015).</li><li>Nirantar, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+Situ+Nanostructural+Analysis+of+Volatile+Threshold+Switching+and+Non-Volatile+Bipolar+Resistive+Switching+in+Mixed-Phased+a-VOx+Asymmetric+Crossbars.">In Situ Nanostructural Analysis of Volatile Threshold Switching and Non-Volatile Bipolar Resistive Switching in Mixed-Phased a-VOx Asymmetric Crossbars.</a> Advanced Electronic Materials. 5 (12), 1900605 (2019).</li><li>Rupp, J. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Different+threshold+and+bipolar+resistive+switching+mechanisms+in+reactively+sputtered+amorphous+undoped+and+Cr-doped+vanadium+oxide+thin+films.">Different threshold and bipolar resistive switching mechanisms in reactively sputtered amorphous undoped and Cr-doped vanadium oxide thin films.</a> Journal of Applied Physics. 123 (4), 044502 (2018).</li><li>Ahmed, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inducing+tunable+switching+behavior+in+a+single+memristor.">Inducing tunable switching behavior in a single memristor.</a> Applied Materials Today. 11, 280-290 (2018).</li><li>Nili, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanoscale+Resistive+Switching+in+Amorphous+Perovskite+Oxide+(a-SrTiO3)+Memristors.">Nanoscale Resistive Switching in Amorphous Perovskite Oxide (a-SrTiO3) Memristors.</a> Advanced Functional Materials. 24 (43), 6741-6750 (2014).</li><li>Ahmed, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transparent+amorphous+strontium+titanate+resistive+memories+with+transient+photo-response.">Transparent amorphous strontium titanate resistive memories with transient photo-response.</a> Nanoscale. 9 (38), 14690-14702 (2017).</li><li>Reuhman-Huisken, M. E., Vollenbroek, F. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+optimized+image+reversal+process+for+half-micron+lithography.">An optimized image reversal process for half-micron lithography.</a> Microelectronic Engineering. 11 (1), 575-580 (1990).</li><li>Taha, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Insulator-metal+transition+in+substrate-independent+VO2+thin+film+for+phase-change+devices.">Insulator-metal transition in substrate-independent VO2 thin film for phase-change devices.</a> Scientific Reports. 7 (1), 17899 (2017).</li><li>Booth, J. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Correlating+the+Energetics+and+Atomic+Motions+of+the+Metal-Insulator+Transition+of+M1+Vanadium+Dioxide.">Correlating the Energetics and Atomic Motions of the Metal-Insulator Transition of M1 Vanadium Dioxide.</a> Scientific Reports. 6, 26391 (2016).</li><li>Lee, S., Ivanov, I. N., Keum, J. K., Lee, H. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Epitaxial+stabilization+and+phase+instability+of+VO2+polymorphs.">Epitaxial stabilization and phase instability of VO2 polymorphs.</a> Scientific Reports. 6, 19621 (2016).</li></ol>

The authors have nothing to disclose.

This paper explains the protocol for in&#160;situ biasing with transmission electron microscopy including the fabrication process for the device, gridbar designing for biasing chip mounting, lamella preparation and mounting on the biasing chip, and TEM with in&#160;situ biasing.
The fabrication methodology of cross-point devices, which can be easily scaled up to crossbar structures, is explained. The Ti capping of vanadium oxide is essential to incorporate amorphous vanadium oxide, because it ...

Resistance change oxide memories are increasingly used as the building block for novel memory and logic architectures due to their compatible switching speed, smaller cell structure, and the ability to be designed in high capacity three-dimensional (3D) crossbar arrays1. To date, multiple switching types have been reported for resistive switching devices2,3. Common switching behaviors for metal oxides are unipolar, bipolar, complementary resistive switching, and volatile threshold switching. Adding on to the complexity, single cell has been reported to show multifunctional resistive switching performance as well4,5,6.
This variability means that nanostructural investigations are needed to understand the origins of different memory behaviors and corresponding switching mechanisms to develop clearly defined condition-dependent switching for practical utility. Commonly reported techniques to understand the switching mechanisms are depth profiling with X-ray photoelectron spectroscopy (XPS)7,8, nanoscale secondary ion mass spectroscopy (nano-SIMS)6, nondestructive photoluminescence spectroscopy (PL)8, electrical characterization of different size and thickness of functional oxide of devices, nanoindentation7, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and electron energy loss spectroscopy (EELS) on cross-sectional lamella in a TEM chamber6,8. All the above techniques have provided satisfactory insights about the switching mechanisms. However, in most of the techniques, more than one sample is required for analysis, including the pristine, electroformed, set, and reset devices, to understand the complete switching behavior. This increases experimental complexity and is time consuming. Additionally, the failure rates are high, because locating a subnanoscale filament in a device a few microns in size is tricky. Therefore, in&#160;situ experiments are important in nanostructural characterizations to understand operation mechanisms, as they provide evidence in real-time experiments.
Presented is a protocol for conducting in&#160;situ TEM with electrical biasing for metal-insulator-metal (MIM) stacks of asymmetric resistive switching cross-point devices. The primary goal of this protocol is to provide a detailed methodology for lamella preparation using a focus ion beam (FIB) and in&#160;situ experimental setup for TEM and electrical biasing. The process is explained using a representative study of asymmetric cross-point devices based on mixed-phased amorphous vanadium oxide (a-VOx)4. Also presented is the fabrication process of cross-point devices incorporating a-VOx, which can be easily scaled up to crossbars, using standard micro-nano fabrication processes. This fabrication process is important as it incorporates in crossbars a-VOx which dissolves in water.
The advantage of this protocol is that with only one lamella, nanostructural changes can be observed in TEM, unlike the other techniques, where a minimum of three devices or lamellae are required. This significantly simplifies the process and reduces time, cost, and effort while providing reliable visual evidence of nanostructural changes in real-time operations. Additionally, it is designed with standard micro-nano fabrication processes, microscopy techniques, and instruments in innovative ways to establish its novelty and address the research gaps.
In the representative study described here for a-VOx-based cross-point devices, the in&#160;situ TEM protocol helps to understand the switching mechanism behind apolar and volatile threshold switching4. The process and methodology developed for observing nanostructural changes in a-VOx during in&#160;situ biasing can be easily extended to in situ temperature, and in situ temperature and biasing simultaneously, by just replacing the lamella mounting chip, and to any other material including two or more layers of functional material in a metal-insulator-metal sandwiched structure. It helps reveal the underlying operation mechanism and explain electrical or thermal characteristics.

<table border="0" cellpadding="0" cellspacing="0" style="width:932px;" width="931">
	<colgroup>
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		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:265px;">Resist processing system</td>
			<td style="width:173px;">EV group</td>
			<td style="width:195px;">EVG 101</td>
			<td style="width:299px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Acetone</td>
			<td style="width:173px;">Chem-Supply</td>
			<td style="width:195px;">AA008</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Biasing Chip - E-chip</td>
			<td style="width:173px;">Protochips</td>
			<td>E-FEF01-A4</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Developer</td>
			<td style="width:173px;">MMRC</td>
			<td style="width:195px;">AZ 400K</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Electron beam evaporator - PVD 75</td>
			<td style="width:173px;">Kurt J Leskar</td>
			<td style="width:195px;">PRO Line - eKLipse</td>
			<td></td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;">Focused Ion beam system</td>
			<td style="width:173px;">Thermo Fisher - FEI</td>
			<td style="width:195px;">Scios DualBeamTM system</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:265px;">Hot plates</td>
			<td style="width:173px;">Brewer Science Inc.</td>
			<td style="width:195px;">1300X</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Magnetron Sputterer</td>
			<td style="width:173px;">Kurt J Leskar</td>
			<td style="width:195px;">PRO Line</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mask aligner</td>
			<td style="width:173px;">Karl Suss</td>
			<td style="width:195px;">MA6</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Maskless Aligner</td>
			<td style="width:173px;">Heildberg instruments</td>
			<td style="width:195px;">MLA150</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:22px;">Methanol</td>
			<td style="width:173px;">Fisher scientific</td>
			<td style="width:195px;">M/4056</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Phototresist</td>
			<td style="width:173px;">MMRC</td>
			<td style="width:195px;">AZ 5412E</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:265px;">Pt source for e-beam evaporator</td>
			<td style="width:173px;">Unicore</td>
			<td style="width:195px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">The Fusion E-chip holder</td>
			<td style="width:173px;">Protochips</td>
			<td style="width:195px;">Fusion 350</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:265px;">Ti source for e-beam evaporator</td>
			<td style="width:173px;">Unicore</td>
			<td style="width:195px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Transmission Electron Microscope</td>
			<td style="width:173px;">JEOL</td>
			<td style="width:195px;">JEM 2100F</td>
			<td></td>
		</tr>
	</tbody>
</table>

in situ transmission electron microscopy with biasing and fabrication of asymmetric crossbars based on mixed-phased a-vox

Resistive switching crossbar architecture is highly desired in the field of digital memories due to low cost and high-density benefits. Different materials show variability in resistive switching properties due to the intrinsic nature of the material used, leading to discrepancies in the field because of underlying operation mechanisms. This highlights a need for a reliable technique to understand mechanisms using nanostructural observations. This protocol explains a detailed process and methodology of in&#160;situ nanostructural analysis as a result of electrical biasing using transmission electron microscopy (TEM). It provides visual and reliable evidence of underlying nanostructural changes in real time memory operations. Also included is the methodology of fabrication and electrical characterizations for asymmetric crossbar structures incorporating amorphous vanadium oxide. The protocol explained here for vanadium oxide films can be easily extended to any other materials in a metal-dielectric-metal sandwiched structure. Resistive switching crossbars are predicted to serve the programmable logic and neuromorphic circuits for next-generation memory devices, given the understanding of the operation mechanisms. This protocol reveals the switching mechanism in a reliable, timely, and cost-effective way in any type of resistive switching materials, and thereby predicts the device&#39;s applicability.

The results achieved using this protocol for the a-VOx cross-point devices are explained in Figure 8. Figure 8A shows the TEM micrograph of the intact lamella. Here the diffraction patterns (inset) indicate the amorphous nature of the oxide film. For the in situ&#160;TEM measurements,&#160;controlled voltages were applied starting from 25&#160;mV to 8&#160;V in 20&#160;mV steps with the bottom electrode (BE) positively biased and top...

Watch this Scientific Journal Video about In Situ Transmission Electron Microscopy with Biasing and Fabrication of Asymmetric Crossbars Based on Mixed-Phased a-VOx at JoVE.com

In Situ Transmission Electron Microscopy with Biasing and Fabrication of Asymmetric Crossbars Based on Mixed-Phased a-VOx

Presented here is a protocol for analyzing nanostructural changes during in&#160;situ biasing with transmission electron microscopy (TEM) for a stacked metal-insulator-metal structure. It has significant applications in resistive switching crossbars for the next generation of programmable logic circuits and neuromimicking hardware, to reveal their underlying operation mechanisms and practical applicability.

In Situ Transmission Electron Microscopy with Biasing and Fabrication of Asymmetric Crossbars Based on Mixed-Phased a-VOx

Resistive switching crossbar architecture is highly desired in the field of digital memories due to low cost and high-density benefits. Different ...

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3.9K Views.  RMIT University. Presented here is a protocol for analyzing nanostructural changes during in situ biasing with transmission electron microscopy (TEM) for a stacked metal-insulator-metal structure. It has significant applications in resistive switching crossbars for the next generation of programmable logic circuits and neuromimicking hardware, to reveal their underlying operation mechanisms and practical applicability.

Video: In Situ Transmission Electron Microscopy with Biasing and Fabrication of Asymmetric Crossbars Based on Mixed-Phased a-VOx

Revealing Dynamic Processes of Materials in Liquids Using Liquid Cell Transmission Electron Microscopy

The recent development for in situ transmission electron microscopy, which allows imaging through liquids with high spatial resolution, has attracted significant interests across the research fields of materials science, physics, chemistry and biology. The key enabling technology is a liquid cell. We fabricate liquid cells with thin viewing windows through a sequential microfabrication process, including silicon nitride membrane deposition, photolithographic patterning, wafer etching, cell bonding, etc. A liquid cell with the dimensions of a regular TEM grid can fit in any standard TEM sample holder. About 100 nanoliters reaction solution is loaded into the reservoirs and about 30 picoliters liquid is drawn into the viewing windows by capillary force. Subsequently, the cell is sealed and loaded into a microscope for in situ imaging. Inside the TEM, the electron beam goes through the thin liquid layer sandwiched between two silicon nitride membranes. Dynamic processes of nanoparticles in liquids, such as nucleation and growth of nanocrystals, diffusion and assembly of nanoparticles, etc., have been imaged in real time with sub-nanometer resolution. We have also applied this method to other research areas, e.g., imaging proteins in water. Liquid cell TEM is poised to play a major role in revealing dynamic processes of materials in their working environments. It may also bring high impact in the study of biological processes in their native environment.

We have developed a self-contained liquid cell, which allows imaging through liquids using a transmission electron microscope. Dynamic processes of nanoparticles in liquids can be revealed in real time with sub-nanometer resolution.

The recent development for in situ transmission electron microscopy, which allows imaging through liquids with high spatial resolution, has attracted ...

In Situ Time-dependent Dielectric Breakdown in the Transmission Electron Microscope: A Possibility to Understand the Failure Mechanism in Microelectronic Devices

The time-dependent dielectric breakdown (TDDB) in on-chip interconnect stacks is one of the most critical failure mechanisms for microelectronic devices. The aggressive scaling of feature sizes, both on devices and interconnects, leads to serious challenges to ensure the required product reliability. Standard reliability tests and post-mortem failure analysis provide only limited information about the physics of failure mechanisms and degradation kinetics. Therefore it is necessary to develop new experimental approaches and procedures to study the TDDB failure mechanisms and degradation kinetics in particular. In this paper, an in situ experimental methodology in the transmission electron microscope (TEM) is demonstrated to investigate the TDDB degradation and failure mechanisms in Cu/ULK interconnect stacks. High quality imaging and chemical analysis are used to study the kinetic process. The in situ electrical test is integrated into the TEM to provide an elevated electrical field to the dielectrics. Electron tomography is utilized to characterize the directed Cu diffusion in the insulating dielectrics. This experimental procedure opens a possibility to study the failure mechanism in interconnect stacks of microelectronic products, and it could also be extended to other structures in active devices.

In Situ Time-dependent Dielectric Breakdown in the Transmission Electron Microscope: A Possibility to Understand the Failure Mechanism in Microelectronic Devices

The time-dependent dielectric breakdown (TDDB) in on-chip interconnect stacks is one of the most critical failure mechanisms for microelectronic devices. This paper demonstrates the procedure of an in situ TDDB experiment in the transmission electron microscope, which opens a possibility to study the failure mechanism in microelectronic products.

The time-dependent dielectric breakdown (TDDB) in on-chip interconnect stacks is one of the most critical failure mechanisms for microelectronic devices. ...

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices have used devices prepared by spin coating, a process that is not amenable to large-scale fabrication. This mismatch in device fabrication makes it difficult to translate quantitative results obtained in the laboratory to the commercial level, making optimization difficult. Using a mini-slot die coater, this mismatch can be resolved by translating the commercial process to the laboratory and characterizing the structure formation in the active layer of the device in real time and in situ as films are coated onto a substrate. The evolution of the morphology was characterized under different conditions, allowing us to propose a mechanism by which the structures form and grow. This mini-slot die coater offers a simple, convenient, material efficient route by which the morphology in the active layer can be optimized under industrially relevant conditions. The goal of this protocol is to show experimental details of how a solar cell device is fabricated using a mini-slot die coater and technical details of running in situ structure characterization using the mini-slot die coater.

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Here, we present a protocol to fabricate organic thin film solar cells using a mini-slot die coater and related in-line structure characterizations using synchrotron scattering techniques.

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices ...

Studying Dynamic Processes of Nano-sized Objects in Liquid using Scanning Transmission Electron Microscopy

Samples fully embedded in liquid can be studied at a nanoscale spatial resolution with Scanning Transmission Electron Microscopy (STEM) using a microfluidic chamber assembled in the specimen holder for Transmission Electron Microscopy (TEM) and STEM. The microfluidic system consists of two silicon microchips supporting thin Silicon Nitride (SiN) membrane windows. This article describes the basic steps of sample loading and data acquisition. Most important of all is to ensure that the liquid compartment is correctly assembled, thus providing a thin liquid layer and a vacuum seal. This protocol also includes a number of tests necessary to perform during sample loading in order to ensure correct assembly. Once the sample is loaded in the electron microscope, the liquid thickness needs to be measured. Incorrect assembly may result in a too-thick liquid, while a too-thin liquid may indicate the absence of liquid, such as when a bubble is formed. Finally, the protocol explains how images are taken and how dynamic processes can be studied. A sample containing AuNPs is imaged both in pure water and in saline.

This protocol describes the operation of a liquid flow specimen holder for scanning transmission electron microscopy of AuNPs in water, as used for the observation of nanoscale dynamic processes.

Samples fully embedded in liquid can be studied at a nanoscale spatial resolution with Scanning Transmission Electron Microscopy (STEM) using a ...

A Method for Obtaining Serial Ultrathin Sections of Microorganisms in Transmission Electron Microscopy

Observing cells and cell components in three dimensions at high magnification in transmission electron microscopy requires preparing serial ultrathin sections of the specimen. Although preparing serial ultrathin sections is considered to be very difficult, it is rather easy if the proper method is used. In this paper, we show a step-by-step procedure for safely obtaining serial ultrathin sections of microorganisms. The key points of this method are: 1) to use the large part of the specimen and adjust the specimen surface and knife edge so that they are parallel to each other; 2) to cut serial sections in groups and avoid difficulty in separating sections using a pair of hair strands when retrieving a group of serial sections onto the slit grids; 3) to use a 'Section-holding loop' and avoid mixing up the order of the section groups; 4) to use a 'Water-surface-raising loop' and make sure the sections are positioned on the apex of the water and that they touch the grid first, in order to place them in the desired position on the grids; 5) to use the support film on an aluminum rack and make it easier to recover the sections on the grids and to avoid wrinkling of the support film; and 6) to use a staining tube and avoid accidentally breaking the support films with tweezers. This new method enables obtaining serial ultrathin sections without difficulty. The method makes it possible to analyze cell structures of microorganisms at high resolution in 3D, which cannot be achieved by using the automatic tape-collecting ultramicrotome method and serial block-face or focused ion beam scanning electron microscopy.

This study presents reliable and easy procedures for obtaining serial ultrathin sections of a microorganism without expensive equipment in transmission electron microscopy.

Observing cells and cell components in three dimensions at high magnification in transmission electron microscopy requires preparing serial ultrathin ...

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of lithium-ion (Li-ion) batteries. However, a number of setbacks prevent their integration into commercial devices. The main limiting factor is due to nanoscale phenomena occurring at the electrode/electrolyte interfaces, ultimately leading to degradation of battery operation. These key problems are highly challenging to observe and characterize as these batteries contain multiple buried interfaces. One approach for direct observation of interfacial phenomena in thin film batteries is through the fabrication of electrochemically active nanobatteries by a focused ion beam (FIB). As such, a reliable technique to fabricate nanobatteries was developed and demonstrated in recent work. Herein, a detailed protocol with a step-by-step process is presented to enable the reproduction of this nanobattery fabrication process. In particular, this technique was applied to a thin film battery consisting of LiCoO2/LiPON/a-Si, and has further been previously demonstrated by in situ cycling within a transmission electron microscope.

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

A protocol for the fabrication of electrochemically active LiPON-based solid-state lithium-ion nanobatteries using a focused ion beam is presented.

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of ...

Fabrication of Flexible Image Sensor Based on Lateral NIPIN Phototransistors

Flexible photodetectors have been intensely studied for the use of curved image sensors, which are a crucial component in bio-inspired imaging systems, but several challenging points remain, such as a low absorption efficiency due to a thin active layer and low flexibility. We present an advanced method to fabricate a flexible phototransistor array with an improved electrical performance. The outstanding electrical performance is driven by a low dark current owing to deep impurity doping. Stretchable and flexible metal interconnectors simultaneously offer electrical and mechanical stabilities in a highly deformed state. The protocol explicitly describes the fabrication process of the phototransistor using a thin silicon membrane. By measuring I-V characteristics of the completed device in deformed states, we demonstrate that this approach improves the mechanical and electrical stabilities of the phototransistor array. We expect that this approach to a flexible phototransistor can be widely used for the applications of not only next-generation imaging systems/optoelectronics but also wearable devices such as tactile/pressure/temperature sensors and health monitors.

We present a detailed method to fabricate a deformable lateral NIPIN phototransistor array for curved image sensors. The phototransistor array with an open mesh form, which is composed of thin silicon islands and stretchable metal interconnectors, provides flexibility and stretchability. The parameter analyzer characterizes the electrical property of the fabricated phototransistor.

Flexible photodetectors have been intensely studied for the use of curved image sensors, which are a crucial component in bio-inspired imaging systems, ...

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic glasses (MGs). Despite their amorphous nature, the identification of hyperfine interactions unveils faint structural modifications. For this purpose, we have employed two techniques that utilize nuclear resonance among nuclear levels of a stable 57Fe isotope, namely M&#246;ssbauer spectrometry and nuclear forward scattering (NFS) of synchrotron radiation. The effects of heat treatment upon (Fe2.85Co1)77Mo8Cu1B14 MG are discussed using the results of ex situ and in situ experiments, respectively. As both methods are sensitive to hyperfine interactions, information on structural arrangement as well as on magnetic microstructure is readily available. M&#246;ssbauer spectrometry performed ex situ describes how the structural arrangement and magnetic microstructure appears at room temperature after the annealing under certain conditions (temperature, time), and thus this technique inspects steady states. On the other hand, NFS data are recorded in situ during dynamically changing temperature and NFS examines transient states. The use of both techniques provides complementary information. In general, they can be applied to any suitable system in which it is important to know its steady state but also transient states.

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

Here, we present a protocol to describe ex situ and in situ investigations of structural transformations in metallic glasses. We employed nuclear-based analytical methods which inspect hyperfine interactions. We demonstrate the applicability of M&#246;ssbauer spectrometry and nuclear forward scattering of synchrotron radiation during temperature-driven experiments.

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic ...

Fabrication of Magnetic Nanostructures on Silicon Nitride Membranes for Magnetic Vortex Studies Using Transmission Microscopy Techniques

Electron and x-ray magnetic microscopies allow for high-resolution magnetic imaging down to tens of nanometers. However, the samples need to be prepared on transparent membranes which are very fragile and difficult to manipulate. We present processes for the fabrication of samples with magnetic micro- and nanostructures with spin configurations forming magnetic vortices suitable for Lorentz transmission electron microscopy and magnetic transmission x-ray microscopy studies. The samples are prepared on silicon nitride membranes and the fabrication consists of a spin coating, UV and electron-beam lithography, the chemical development of the resist, and the evaporation of the magnetic material followed by a lift-off process forming the final magnetic structures. The samples for the Lorentz transmission electron microscopy consist of magnetic nanodiscs prepared in a single lithography step. The samples for the magnetic x-ray transmission microscopy are used for time-resolved magnetization dynamic experiments, and magnetic nanodiscs are placed on a waveguide which is used for the generation of repeatable magnetic field pulses by passing an electric current through the waveguide. The waveguide is created in an extra lithography step.

A protocol for the fabrication of magnetic micro- and nanostructures with spin configurations forming magnetic vortices suitable for transmission electron microscopy (TEM) and magnetic transmission x-ray microscopy (MTXM) studies is presented.

Electron and x-ray magnetic microscopies allow for high-resolution magnetic imaging down to tens of nanometers. However, the samples need to be prepared ...

Single-Digit Nanometer Electron-Beam Lithography with an Aberration-Corrected Scanning Transmission Electron Microscope

We demonstrate extension of electron-beam lithography using conventional resists and pattern transfer processes to single-digit nanometer dimensions by employing an aberration-corrected scanning transmission electron microscope as the exposure tool. Here, we present results of single-digit nanometer patterning of two widely used electron-beam resists: poly (methyl methacrylate) and hydrogen silsesquioxane. The method achieves sub-5 nanometer features in poly (methyl methacrylate) and sub-10 nanometer resolution in hydrogen silsesquioxane. High-fidelity transfer of these patterns into target materials of choice can be performed using metal lift-off, plasma etch, and resist infiltration with organometallics.

We use an aberration-corrected scanning transmission electron microscope to define single-digit nanometer patterns in two widely-used electron-beam resists: poly (methyl methacrylate) and hydrogen silsesquioxane. Resist patterns can be replicated in target materials of choice with single-digit nanometer fidelity using liftoff, plasma etching, and resist infiltration by organometallics.

We demonstrate extension of electron-beam lithography using conventional resists and pattern transfer processes to single-digit nanometer dimensions by ...