Name: in situ transmission electron microscopy with biasing and fabrication of asymmetric crossbars based on mixed-phased a-vox
Uploaded: 2020-05-13T13:00:00
Description: 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

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:
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		<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, develo...

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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.

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			<td height="21" style="height:21px;width:265px;">Resist processing system</td>
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			<td height="21" style="height:21px;">Biasing Chip - E-chip</td>
			<td style="width:173px;">Protochips</td>
			<td>E-FEF01-A4</td>
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			<td height="21" style="height:21px;">Developer</td>
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			<td style="width:195px;">AZ 400K</td>
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			<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>
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			<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>
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			<td height="21" style="height:21px;">Magnetron Sputterer</td>
			<td style="width:173px;">Kurt J Leskar</td>
			<td style="width:195px;">PRO Line</td>
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			<td height="21" style="height:21px;">Mask aligner</td>
			<td style="width:173px;">Karl Suss</td>
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			<td height="21" style="height:21px;">Maskless Aligner</td>
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			<td height="21" style="height:22px;">Methanol</td>
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			<td height="21" style="height:21px;">Phototresist</td>
			<td style="width:173px;">MMRC</td>
			<td style="width:195px;">AZ 5412E</td>
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			<td height="21" style="height:21px;width:265px;">Pt source for e-beam evaporator</td>
			<td style="width:173px;">Unicore</td>
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			<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>
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			<td height="21" style="height:21px;width:265px;">Ti source for e-beam evaporator</td>
			<td style="width:173px;">Unicore</td>
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			<td height="21" style="height:21px;">Transmission Electron Microscope</td>
			<td style="width:173px;">JEOL</td>
			<td style="width:195px;">JEM 2100F</td>
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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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