Name: the effect of anodization parameters on the aluminum oxide dielectric layer of thin-film transistors
Uploaded: 2020-05-24T13:00:00
Description: Watch this Scientific Journal Video about The Effect of Anodization Parameters on the Aluminum Oxide Dielectric Layer of Thin-Film Transistors at JoVE.com

The authors acknowledge the financial support from S&#227;o Paulo Research Foundation &#8211; FAPESP &#8211; Brazil (grants 19/05620-3, 19/08019-9, 19/01671-2, 16/03484-7 and 14/13904-8) and Research Collaboration Program Newton Fund from Royal Academy of Engineering. Authors also acknowledge the technical support from B. F. da Silva, J.P. Braga, J.B. Cantuaria, G.R. de Lima and G.A. de Lima Sobrinho and Prof. Marcelo de Carvalho Borba&#8217;s group (IGCE/UNESP) for providing the filming equipment.

The protocol described in the present work is separated into: i) preparation of the electrolytic solution for anodization; ii) substrate cleaning and preparation; iii) anodization process; iv) deposition of the TFT active layer and drain/source electrodes; v) TFT electrical characterization and analysis and vi) application of ANOVA to determine the significance of the manufacturing factors in the TFT mobility.
1. Preparation of the electrolytic solution for anodization
<ol>
	<li>Perform all ...

<ol>
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C., Kumar, D., Fugikawa-Santos, L., Alves, N., Kettle, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optimization+of+the+Anodization+Processing+for+Aluminum+Oxide+Gate+Dielectrics+in+ZnO+Thin+Film+Transistors+by+Multivariate+Analysis.">Optimization of the Anodization Processing for Aluminum Oxide Gate Dielectrics in ZnO Thin Film Transistors by Multivariate Analysis.</a> ACS Combinatorial Science. , (2019).</li><li>Min, L., 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=Dual+Gate+Indium-Zinc+Oxide+Thin-Film+Transistors+Based+on+Anodic+Aluminum+Oxide+Gate+Dielectrics.">Dual Gate Indium-Zinc Oxide Thin-Film Transistors Based on Anodic Aluminum Oxide Gate Dielectrics.</a> IEEE Transactions on Electron Devices. 61 (7), 2448-2453 (2014).</li><li>Liu, 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=Eco-friendly+water-induced+aluminum+oxide+dielectrics+and+their+application+in+a+hybrid+metal+oxide/polymer+TFT.">Eco-friendly water-induced aluminum oxide dielectrics and their application in a hybrid metal oxide/polymer TFT.</a> RSC Advances. 5 (105), 86606-86613 (2015).</li><li>Berndt, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anodization+of+Aluminum+in+Highly+Viscous+Phosphoric+Acid.+PART+2:+Investigation+of+Anodic+Oxide+Formation+and+Dissolution+Rates.">Anodization of Aluminum in Highly Viscous Phosphoric Acid. PART 2: Investigation of Anodic Oxide Formation and Dissolution Rates.</a> International Journal of Electrochemical Science. , 9531-9550 (2018).</li><li>Huang, S. Z., Hwu, J. 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The anodization process used to obtain the dielectric has a strong influence on the performance of the TFTs fabricated, keeping constant all geometrical parameters and the fabrication parameters of the active. For the TFT mobility, which is one of the most important performance parameters for TFTs, it can vary more than 2 orders of magnitude by changing the manufacturing factors in the range given by Table I. Therefore, the careful control of the anodization parameters is of great importance when fabricating devices comp...

Flexible, printed and large area electronics represent an emerging market that is expected to attract billions of dollars in investments in upcoming years. To achieve the hardware requirements for the new generation of smartphones, flat panel displays and internet-of-things (IoT) devices, there is a huge demand for materials that are lightweight, flexible and with optical transmittance in the visible spectrum without sacrificing speed and high performance. A key point is to find alternatives to amorphous silicon (a-Si) as the active material of the thin-film transistors (TFTs) used in the drive circuits of most of the current active-matrix displays (AMDs). a-Si has low compatibility to flexible and transparent substrates, presents limitations to large-area processing, and has a carrier mobility of about 1 cm2&#8729;V-1&#8729;s-1, which cannot meet the needs of resolution and refresh rate for next generation displays. Semiconducting metal oxides (SMOs) such as zinc oxide (ZnO)1,2,3, indium zinc oxide (IZO)4,5 and indium gallium zinc oxide (IGZO)6,7 are good candidates to replace a-Si as the active layer of TFTs because they are highly transparent in the visible spectrum, are compatible to flexible substrates and large area deposition and can achieve mobilities as high as 80 cm2&#8729;V-1&#8729;s-1. Moreover, SMOs can be processed in a variety of methods: RF sputtering6 , pulsed laser deposition (PLD)8, chemical vapor deposition (CVD)9, atomic layer deposition (ALD)10, spin-coating11, ink-jet printing12 and spray-pyrolysis13.
However, few challenges such as the control of intrinsic defects, air/UV stimulated instabilities and formation of semiconductor/dielectric interface localized states still need to be overcome to enable the large-scale manufacturing of circuits comprising SMO-based TFTs. Among the desired characteristics of high performance TFTs, one can mention the low power consumption, low operation voltage, low gate leakage current, threshold voltage stability and wideband frequency operation, which are extremely dependent on the gate dielectrics (and the semiconductor/insulator interface as well). In this sense, high-&#954; dielectric materials14,15,16 are particularly interesting since they provide large values of capacitance per unit area and low leakage currents using relatively thin films. Aluminum oxide (Al2O3) is a promising material for the TFT dielectric layer since it presents a high dielectric constant (from 8 up to 12), high dielectric strength, high electrical resistivity, high thermal stability and can be processed as extremely thin and uniform films by several different deposition/growth techniques15,17,18,19,20,21. Additionally, aluminum is the third most abundant element in the Earth&#8217;s crust, what means that it is easily available and relatively cheap compared to other elements used to produce high-k dielectrics.
Although deposition/growth of Al2O3 thin (below 100 nm) films can be successfully attained by techniques such as RF magnetron sputtering, chemical vapor deposition (CVD), atomic layer deposition (ALD), the growth by anodization of a thin metallic Al layer17,18,21,22,23,24,25,26 is particularly interesting for flexible electronics owing to its simplicity, low cost, low temperature, and film thickness control in nanometric scale. Besides, anodization has a great potential for roll-to-roll (R2R) processing, which can be easily adapted from processing techniques already being used at industrial level, permitting quick manufacturing upscaling.
Al2O3 growth by anodization of metallic Al can be described by the following equations
2Al + 3 / 2 02 &#8594; Al2O3&#160; &#160; &#160; (1)
2Al + 3H2O &#8594; Al2O3 + 3H2&#160; &#160; &#160; (2)
where the oxygen is provided by the dissolved oxygen in the electrolyte solution or by the adsorbed molecules at the film surface, whereas the water molecules are promptly available from the electrolyte solution. The anodized film roughness (which affects the TFT mobility due to carrier scattering at the semiconductor/dielectric interface) and the density of localized states at the semiconductor/dielectric interface (which affects the TFT threshold voltage and electrical hysteresis) are strongly dependent on anodization process parameters, to name a few: the water content, the temperature and the pH of the electrolyte24,27. Other factors related to the Al layer deposition (like evaporation rate and metal thickness) or to post-anodization processes (like annealing) can also influence the electrical performance of fabricated TFTs. The effect of these multiple factors on response parameters can be studied by varying each factor individually while keeping all other factors constant, which is an extremely time-consuming and inefficient task. Design of experiments (DOE), on the other hand, is a statistical method based on the simultaneous variation of multiple parameters, which permits the identification of the most significant factors on a system/device performance response by using a relatively reduced number of experiments28.
Recently, we have used multivariate analysis based on a Plackett-Burman29 DOE to analyze the effects of Al2O3 anodization parameters on the performance of sputtered ZnO TFTs18. The results were used to find the most significant factors for several different response parameters and applied to the optimization of the device performance changing only parameters related to the anodization process of the dielectric layer.
The current work presents the whole protocol for manufacturing TFTs using anodized Al2O3 films as gate dielectrics, as well a detailed description for the study of the influence of the multiple anodization parameters on the device electrical performance by using a Plackett-Burman DOE. The significance of the effects on TFT response parameters such as the carrier mobility is determined by performing analysis of variance (ANOVA) to the results obtained from the experiments.

<table border="0" cellpadding="0" cellspacing="0" style="width:1393px;" width="1393">
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		<col />
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		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="23">
			<td height="23" style="height:23px;width:299px;">Acetone</td>
			<td style="width:212px;">LabSynth</td>
			<td style="width:161px;">A1017</td>
			<td style="width:721px;">ACS reagent grade</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:299px;">Aluminum (Al) Wire Evaporation</td>
			<td style="width:212px;">Kurt J. Lesker Company</td>
			<td style="width:161px;">EVMAL40060</td>
			<td>1.5 mm (0.060&#34;) Dia.; 1lb; 99.99%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:299px;">Ammonium hydroxide solution</td>
			<td style="width:212px;">Sigma Aldrich</td>
			<td style="width:161px;">338818</td>
			<td>ACS reagent, 28.0-30.0% NH3 basis</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:299px;">Chemoface - Software to set a design of experiment (DOE)</td>
			<td style="width:212px;">Federal University of Lavras (UFLA), Brazil</td>
			<td style="width:161px;"></td>
			<td>Free software developed by Federal University of Lavras (UFLA), Brazil - http://www.ufla.br/chemoface/</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:299px;">Cleaning detergent</td>
			<td style="width:212px;">Sigma Aldrich</td>
			<td style="width:161px;">Alconox</td>
			<td>Alkaline detergent for substrate cleaning</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:299px;">Ethylene glycol</td>
			<td style="width:212px;">Sigma Aldrich</td>
			<td style="width:161px;">102466</td>
			<td>ReagentPlus, &#8805;99%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:299px;">Isopropanol</td>
			<td style="width:212px;">LabSynth</td>
			<td style="width:161px;">A1078</td>
			<td>ACS reagent grade</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:299px;">Glass substrates</td>
			<td style="width:212px;">Sigma Aldrich</td>
			<td style="width:161px;">CLS294775X50</td>
			<td>Corning microscope slides, plain</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:299px;">L-(+)-Tartaric acid</td>
			<td style="width:212px;">Sigma Aldrich</td>
			<td style="width:161px;">T109</td>
			<td>&#8805;99.5%</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:299px;">Mechanical shadow mask for deposition of the sputtered ZnO active layer</td>
			<td style="width:212px;">Lasertools, Brazil</td>
			<td style="width:161px;">custom mask</td>
			<td>10 mm x 10 mm square.</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:299px;">Mechanical shadow mask for TFT gate electrode</td>
			<td style="width:212px;">Lasertools, Brazil</td>
			<td style="width:161px;">custom mask</td>
			<td>25 mm long stripe, 3 mm wide.</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:299px;">Mechanical shadow mask for TFT source/drain electrodes</td>
			<td style="width:212px;">Lasertools, Brazil</td>
			<td style="width:161px;">custom mask</td>
			<td>100 &#181;m stripes, separated by 100 &#181;m gap, overlapping of 5 mm</td>
		</tr>
		<tr height="29">
			<td height="29" style="height:29px;width:299px;">Plasma cleaner</td>
			<td style="width:212px;">MTI</td>
			<td style="width:161px;">PDC-32G</td>
			<td>Campact plasma cleaner with vacuum pump</td>
		</tr>
		<tr height="51">
			<td height="51" style="height:51px;width:299px;">Sputter coating system</td>
			<td style="width:212px;">HHV</td>
			<td style="width:161px;">Auto 500</td>
			<td>RF sputtering system with thickness and deposition rate control</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:299px;">Stiring plate</td>
			<td style="width:212px;">Sun Valley</td>
			<td style="width:161px;">MS300</td>
			<td>Stiring plate with heating control</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:299px;">Thermal evaporator</td>
			<td style="width:212px;">HHV</td>
			<td style="width:161px;">Auto 306</td>
			<td>it has a high precision sensor for measure the thickness and rate of deposition of thin films</td>
		</tr>
		<tr height="30">
			<td height="30" style="height:30px;width:299px;">Two-channel source-measuring unit</td>
			<td style="width:212px;">Keithley</td>
			<td style="width:161px;">2410</td>
			<td>Keithley model 2410 or similar/for anodization process</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:299px;">Two-channel source-measuring unit</td>
			<td style="width:212px;">Keithley</td>
			<td style="width:161px;">2612B</td>
			<td>Dual channel source-measure unit (SMU) for TFT measurements</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:299px;">Ultrasonic bath</td>
			<td style="width:212px;">Soni-tech</td>
			<td style="width:161px;">Soni-top 402A</td>
			<td>Ultrasonic bath with heating control</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:299px;">Zinc Oxide (ZnO) Sputtering Targets</td>
			<td style="width:212px;">Kurt J. Lesker Company</td>
			<td style="width:161px;">EJTZNOX304A3</td>
			<td>3.0&#34; Dia. x 0.250&#34; Thick; 99.9%</td>
		</tr>
	</tbody>
</table>

the effect of anodization parameters on the aluminum oxide dielectric layer of thin-film transistors

Aluminum-oxide (Al2O3) is a low cost, easily processable and high dielectric constant insulating material that is particularly appropriate for use as the dielectric layer of thin-film transistors (TFTs). Growth of aluminum-oxide layers from anodization of metallic aluminum films is greatly advantageous when compared to sophisticated processes such as atomic layer deposition (ALD) or deposition methods that demand relatively high temperatures (above 300 &#176;C) such as aqueous combustion or spray-pyrolysis. However, the electrical properties of the transistors are highly dependent on the presence of defects and localized states at the semiconductor/dielectric interface, which are strongly affected by the manufacturing parameters of the anodized dielectric layer. To determine how several fabrication parameters influence the device performance without performing all possible combination of factors, we used a reduced factorial analysis based on a Plackett-Burman design of experiments (DOE). The choice of this DOE permits the use of only 12 experimental runs of combinations of factors (instead of all 256 possibilities) to obtain the optimized device performance. The ranking of the factors by the effect on device responses such as the TFT mobility is possible by applying analysis of variance (ANOVA) to the obtained results.

Eight different aluminum oxide layer manufacture parameters were used as the fabrication factors which we used to analyze the influence on the TFT performance. These factors are enumerated in Table 1, where the corresponding &#8220;low&#8221; (-1) and &#8220;high&#8221; (+1) values for the two-level factorial DOE are presented.
For simplicity, each manufacturing factor was named by a capital letter (A, B, C, etc.) and the corresponding &#8220;low&#8221; or &#8220;high&#8221; l...

Watch this Scientific Journal Video about The Effect of Anodization Parameters on the Aluminum Oxide Dielectric Layer of Thin-Film Transistors at JoVE.com

The Effect of Anodization Parameters on the Aluminum Oxide Dielectric Layer of Thin-Film Transistors

Anodization parameters for growth of the aluminum-oxide dielectric layer of zinc-oxide thin-film transistors (TFTs) are varied to determine the effects on the electrical parameter responses. Analysis of variance (ANOVA) is applied to a Plackett-Burman design of experiments (DOE) to determine the manufacturing conditions that result in optimized device performance.

Aluminum-oxide (Al2O3) is a low cost, easily processable and high dielectric constant insulating material that is particularly appropriate for use as the ...

Here is the overview of the protocol. We start by preparing the electrolytic solution, mixing water, ethylene glycol, and tartaric acid. After that, the substrate glass slides need to be cleaned by sonication in alkaline detergent solution, acetone and isopropanol followed by RF plasma cleaning.The construction of the TFT is done by depositing an aluminium electrode onto the clean glass substrates. Followed by anodization into aluminum oxide sputtering of the zinc oxide active layer and thermal evaporation the drain source electrodes. The aluminum anodization process is carried out by submerging the aluminium coated glass substrate and a gold plated, stainless steel sheet connected to a source measure unit.The process starts by applying constant current in the system with a voltage increasing linearly until the final voltage which determines the oxide thickness. Therefore, the voltage is maintained constant until the current across the system drops to zero. The Electrical characterization of the TFTs is performed by connecting a dual channel source-measuring unit to the gate, drain and source electrodes.The transfer curve is obtained by varying the gate voltage at a constant drain source voltage and measuring the drain source current. The electrical mobility can be determined from the TFT transfer curve. The Placket-Burman design of experiments is performed by labeling the Anodization factors, whichever ride from a low to a high level, determined from the experimental conditions.The Placket-Burman matrix is composed by twelve experimental runs, which correspond to different combinations of the Anodization factors in the predetermined levels. We present here in a protocol to build the zinc oxide tin-filled transistors using anodized aluminum oxide as a gate dielectric layer. We show that it's possible to optimize the performance of TFTS by varying only the anodization process parameters of the gate dielectrics.The electrolytic solution is prepared by mixing 84 mL of ethylene glycol to 1.5 g of tartaric acid. Therefore, add 16 mL of deionized water to the solution, shake gently the solution. After that, stir the solution for approximately 30 minutes until complete dissolution of tartaric acid.Prepare two stocks solutions from ammonia hydroxide to adjust the pH of the electrolyte. The more concentrated solution can be about 28%and the less concentrated about 2%Make the coarse adjustment of the pH using the more concentrated ammonium hydroxide solution. When the pH is close to the desired value, five or six, use the less concentrated solution to finely adjust the pH.The Substrate cleaning procedure starts by sonicating the glass substrates in alkaline detergent solution, 5%in volume at 16 degrees Celsius for 50 minutes. After that, the substrates are rinsed abundantly in deionized water to remove any residues. Dry the substrate by blowing with clean, dry air or nitrogen.The dried substrates are sonicated again in acetone for five minutes. Remove from acetone and dry again in clean dry air or nitrogen. Sonicate once more in isopropanol for five minutes.Remove from isopropanol and repeat the drying procedure. Load the substrates into a RF plasma cleaner and evacuate the chamber. When vacuum is achieved, turn on the RF at medium power and leave for five minutes to finish the cleaning procedure.Remove the substrates from the plasma cleaner and load them into a sample holder with appropriate shadow masks for thermal evaporation of the aluminum gate electrode. The shadow mask, is a stainless laser cut sheet which determines the aluminum gate electrode area. Insert the glass slides into the thermal evaporation chamber and start the deposition procedure.Deposit the aluminum gate electrode with fine control of the evaporation rate and the final thickness of the film. After the evaporation, remove the samples from the chamber. And check if the electrodes were properly deposited.The anodization of the aluminum gate electrode starts by connecting the aluminum coated glass slide and the gold plated stainless steel sheet to the clip connectors. Therefore, the electrodes are submerged into the electrolytic solution and the cables are connected to the Source-Measure Unit. Apply constant current to the electrodes.The voltage drop has to increase linearly, demonstrating that the aluminum oxide growth is occurring properly. When the established final voltage is achieved, switch the SMU to constant voltage mode and wait until the current drops to zero. After finishing the anodization procedure, rinse abundantly the substrate in deionized water.And finish by drying the substrate in dry, clean air or nitrogen. The deposition of the transistor active layer is performed by inserting the substrate with the anodized aluminum oxide layer into appropriate shadow masks. The masks would permit the selective covering of zinc oxide during the sputtering deposition.Insert the samples into this sputtering chamber and initiate the deposition process. Control the sputtering deposition rate and the final thickness of the TFT active layer. After sputtering deposition, remove the samples from the chamber and prepare them for thermal evaporation of the drain and source electrodes.The transistor fabrication is concluded by evaporating the aluminum drain and source electrodes by thermal evaporation using appropriate shadow masks. The used mask design allows the fabrication of three transistors in each substrate. Insert the samples into the evaporation chamber and initiate the deposition procedure.After the evaporation of the aluminum drain and source electrodes, remove the samples from the chamber. Remove the samples from the masks and check the electrodes. The transistors are ready for electrical characterization.The electrical characterization of the TFT is performed by making the contact to the drain, source and gate electrodes using spring probe connectors. The electrodes are therefore connected to a dual channel source and measure unit. The transistor characteristic curves are obtained by polarizing the drain and source electrodes, as well as the gate electrode and measuring the channel current.The analysis of the TFT electrical parameters is carried out by plotting the TFT transfer curve and the square root of the drain current as a function of the gate voltage. The slope of the curve permits the determination of the device mobility. The intercept of the slope of the curve with the X-axis defines the TFT threshold voltage.The analysis of the results obtained the curvature of Placket-Burman design of experiments, can be performed by an analysis software such as Chemoface. Choose the experimental design and enter with the input data. Therefore, calculate the corresponding effects for each anodization parameters and analyze the results by plotting the data in a Pareto chart of effects.The Pareto chart, allows you to rank the anodization factors by the effect on a specific device response parameter such as the TFT mobility. So Placket-Burman is useful for a number of different reasons. Firstly, it allows you to study a number of different factors, systematically and simultaneously.And using statistical approaches such as ANOVA and regression, it allows you to quantify and, understand the most significant factors and the least significant factors which are affecting the anodization process. So we think that the Placket-Burman approach is very valuable in printed electronics. It allows you to rapidly and effectively screen a number of different factors and optimize the factors in a very systematic and quick manner.Although we've developed this approach for anodization, it could be used in many many other areas within printed electronic development.

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