In Situ Transmission Electron Microscopy with Biasing and Fabrication of Asymmetric Crossbars Based on Mixed-Phased a-VOx
May 13th, 2020
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.
In this protocol, we are showing the fabrication process of cross-point devices incorporating amorphous vanadium oxide, which actually dissolves in the water.And further, this protocol helps us to improve our understanding of nano-structural changes during the biasing operations.This protocol allows a visual analysis of nano-structural changes related to device biasing, and can be extended to any metal-insulator-metal device structure that's compatible with high vacuum.This protocol can be easily extended to do in-situ temperature or temperature and biasing together analysis to reveal the atomic level changes happening within the device.To pattern the bottom of the electrode of the cross-point device with photoresist, first spin coat the photoresist onto the wafer at 3000 revolutions per minute, before soft baking at 95 degrees Celsius for 60 seconds.Next, use a 405 nanometer laser to expose the device to 25 millijoules per square centimeter, and bake at 120 degrees Celsius for 120 seconds.Use a 400 nanometer laser to flood-expose the device with 21 milliwatts per square centimeter, and use developer to develop the pattern.Rinse the device with de-ionized water, and use a physical vapor deposition system to deposit 10 nanometers of titanium and 100 nanometers of platinum onto the substrate pattern on layer one.To lift off the deposited metals, place the substrate in an acetone bath for approximately 20 minutes before applying ultrasonic vibrations for two minutes and rinsing with acetone and isopropyl alcohol.Repeat the process until the clean-patterned wafers are achieved.Repeat the same photolithography, or patterning process, to pattern the second layer of amorphous vanadium oxide and the third layer onto the top of the electrode with 20 nanometer titanium and 200 nanometer platinum.For mounting of the biasing chip, first clean the chip in a glass Petri dish filled with acetone with gentle rotation for two minutes.After washing, transfer the chip into a Petri dish filled with methanol for an additional two minutes of rotation before blowing the chip dry with low-pressured nitrogen.Align the dried-biasing chip in square trenches of gridbar, and use screws to fix the grid cover onto the biasing chip, finalizing the placement of the e-chip on the gridbar.To mount the biasing chip with lamella, use conductive carbon tape to mount the newly-prepared sample onto a metal stub, and load the stub into a Focused Ion Beam chamber.Apply additional tape on the sample for grounding to avoid charging issues, and load the biasing chip-mounted gridbar in the chamber at a 52 degree angle.Use the microscope physical control panel and software to focus, as and align the electron beam on a sample surface, and check the eucentric height of the focused sample location and beam coincidence for the electron and ion beams.Click the AutoTem program to run the program on the focused sample location, and use silicone milling to create cross-fiducial alignment markers.Deposit a 1.5 micrometer thick carbon protective layer over the 20/5 micrometer area between the alignment markers, and use a 5 nanoangstrom beam current to mill trenches on either side of the carbon protective layer.Thin the lamella with subsequent 1 nanoangstrom and a 300 picoangstrom ion beam currents to reach a 1 micrometer thickness.Tilt the sample to seven degrees to perform a J-cut on the lamella for separation from the substrate.To attach the lamella to the manipulator needle, tilt the sample to zero degrees and use platinum to attach the lamella to the needle.After attaching to the micro manipulator, use a final cut to separate the lamella from the substrate and slowly retract the micro manipulator.Focus the beam on the top edge of the biasing chip on the gridbar, and use the needle to bring the lamella slowly toward the biasing chip.Align the lamella in the center of the 17 micrometer gap on the top edge of the biasing chip, and slowly move the gap down until it barely touches the chip surface.Use platinum to weld the bottom edges of the lamella to the chip, and use Silicon milling to cut the micro manipulator free from the lamella.Retract the micro manipulator, and connect the top edges of the lamella with platinum traces to the two electrodes of the biasing chip.Tilting the specimen front and back by two degrees to ensure parallel faces and a uniform thickness.Use a consecutive 300 picoangstrom and 100 picoangstrom beam to thin the center region of the lamella to less than 100 nanometers thick.Polish out the ion beam-damaged layer with the gallium-beam accelerating voltage of five kilovolts at a five degree angle to the surface on both faces, and use isolation cuts in the thinned region to remove the short connection between the top and bottom electrodes of the device to create a current path from the bottom to the top electrode through the active region.Then, mount the biasing chip with the lamella on the biasing chip holder, and load the biasing chip holder into the Transmission Electron Microscopy chamber.For in-situ Transmission Electron Microscopy Imaging, carefully connect the wires from the biasing chip holder to the source meter and a control computer.When the Transmission Electron Microscopy chamber pressure drops to the desired value, use the Transmission Electron Microscopy control knobs to focus and align the electron beam on a cross-section of the lamella surface, and apply voltage sweeps, collecting the Transmission Electron Microscopy micrographs in-situ.In-situ nano-structural changes occurring within the lamella on the application of bias can then be observed.In this image, a representative Transmission Electron Microscopy micrograph of the intact lamella can be observed.The diffraction patterns in the inset indicate the amorphous nature of the oxide film.At four volts, a localized crystalline region forms in the oxide layer.In this analysis, d-spacing was 0.35 nanometers, corresponding to the 011 plane of the vanadium oxide M1 phase.At five volts, multiple localized crystal islands oriented in different directions with respect to the substrate can be observed within the oxide.A d-spacing of 0.27 nanometers corresponding to the vanadium oxide A phase and a d-spacing of 0.26 nanometers corresponding to the vanadium oxide M1 phase are apparent.At six volts, moir
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Overview
This protocol outlines the analysis of nanostructural changes during in situ biasing using transmission electron microscopy (TEM) for a stacked metal-insulator-metal structure. The findings have important implications for resistive switching crossbars in programmable logic circuits and neuromimicking hardware.
Key Study Components
Area of Science
- Nanostructural analysis
- Transmission electron microscopy
- Resistive switching technology
Background
- Understanding nanostructural changes is crucial for advancing electronic materials.
- Transmission electron microscopy provides high-resolution imaging of materials.
- Resistive switching crossbars are key components in modern electronic devices.
- Neuromimicking hardware aims to replicate neural processes for computing.
Purpose of Study
- To analyze the nanostructural changes in metal-insulator-metal structures.
- To explore the mechanisms behind resistive switching.
- To assess the practical applicability of these structures in future technologies.
Methods Used
- In situ biasing during transmission electron microscopy.
- Characterization of structural changes at the nanoscale.
- Analysis of electrical properties related to resistive switching.
- Comparative studies of different material configurations.
Main Results
- Identification of key nanostructural changes during biasing.
- Demonstration of the relationship between structure and resistive switching behavior.
- Insights into the operational mechanisms of programmable logic circuits.
- Potential applications in neuromimicking hardware highlighted.
Conclusions
- The study provides a comprehensive protocol for analyzing nanostructures.
- Findings contribute to the understanding of resistive switching mechanisms.
- Implications for future electronic device design and functionality are significant.
Frequently Asked Questions
Executive Industry Relevance
Understanding nanoscale structural dynamics during electrical biasing is critical for de-risking resistive switching materials in next-generation memory and neuromorphic computing platforms. This protocol enables direct visualization of phase transitions and crystalline island formation under bias, providing mechanistic insights that support target validation and predictive confidence in material selection for crossbar architectures. By linking applied voltage to observable nanostructural changes, the method reduces ambiguity in structure-function relationships, informing early discovery decisions for programmable logic and AI hardware applications.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Enables interrogation of thermodynamic and kinetic pathways of phase transformation in resistive switching materials under operational bias.
- Operational Value: Provides reproducible, real-time nanoscale evidence to validate hypotheses about switching mechanisms and material stability.
- Predictive Value: Supports mechanistic de-risking by correlating applied voltage thresholds with crystalline phase formation (e.g., M1 and A phases) in vanadium oxide.
Screening & Assay Development
- Scientific Value: Generates quantitative, bias-dependent structural readouts (e.g., d-spacing measurements) that can serve as functional assays for material screening.
- Operational Value: Establishes a standardized platform for comparing resistive switching behaviors across different metal-insulator-metal compositions.
- Scalability: Protocol is extensible to other materials and environmental conditions (e.g., combined temperature and biasing) for broad assay reuse.
Translational & Preclinical Research
- Translational Continuity: Bridges discovery-phase mechanistic insights with preclinical evaluation by establishing structure-property relationships under device-relevant operating conditions.
- Risk-Adjusted Advancement: Enables go/no-go decisions based on direct observation of filament formation, phase segregation, or interfacial changes that impact device reliability and endurance.
- Biomarker Alignment: Structural signatures (e.g., crystalline island orientation, moiré patterns) can inform translational biomarkers for switching uniformity and device yield.
Pipeline & Workflow Integration
The method fits within the discovery-to-preclinical continuum by enabling hypothesis-driven analysis of switching mechanisms, assay-ready structural profiling, and data-driven material selection for neuromorphic and logic-in-memory applications.
- Discovery Biology: Supports hypothesis testing of ion migration, phase nucleation, and interfacial reactions during biasing, reducing mechanistic ambiguity in target validation.
- Screening: Delivers assay-ready, quantitative outputs such as crystalline phase identification and lattice spacing shifts under defined voltage sweeps.
- Analytics: Provides correlative electrical and structural datasets (e.g., I-V curves with concurrent TEM imaging) that enable multi-parametric comparison of material candidates.
- Translational Research: Connects nanoscale switching dynamics to device-level performance metrics, supporting preclinical continuity for neuromorphic circuit validation.
- Enterprise Reuse: Framework is adaptable to various resistive switching materials and environmental stimuli, promoting cross-platform standardization and long-term utility.
Operational & Enterprise Impact
- Scientific Value: Enhances predictive confidence in material behavior by directly linking nanostructural evolution to resistive switching events.
- Operational Value: Ensures reproducibility and standardization in nanoscale characterization through defined biasing, sample preparation, and imaging protocols.
- Strategic Value: Improves capital efficiency by reducing late-stage failure risk through early mechanistic de-risking of switching materials.
- Portfolio Impact: Enables risk-adjusted prioritization of material candidates based on observed structural stability, switching uniformity, and phase purity under bias.
Implementation Considerations
- Requires expertise in nanofabrication, FIB sample preparation, and in situ TEM biasing techniques.
- Dependent on access to transmission electron microscopy with biasing holders, electron and ion beam capabilities, and vacuum-compatible sample stages.
- Necessitates cross-team standardization between materials science, device engineering, and microscopy teams for consistent sample handling and data interpretation.
- Adaptation considerations include material compatibility with high vacuum, resistance to electron beam damage, and stability of amorphous phases under biasing.
- Practical limitations include sample thickness constraints for electron transparency and potential artifacts from ion beam milling or carbon deposition.
Biopharma FAQs
Chapters in this video
0:04
Introduction
0:52
Fabrication Process and Electrical Characterization
2:33
Biasing Chip Mounting on Gridbar
3:14
Lamella Preparation and Biasing Chip Mounting
6:50
In Situ Transmission Electron Microscopy (TEM)
7:42
Results: Representative In Situ Electrical TEM
9:04
Conclusion
