Thermal Cycling Reliability of Vanadium Dioxide Films for Switching Applications
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Date
2020-12
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The Ohio State University
Abstract
Vanadium dioxide (VO2) is a phase change material that rapidly changes from an
electrical insulator to a conductor at 68 C. Because of this property, VO2 has recently been applied in different fields as a thermally activated switch. However, while voltage-activated and current-activated reliability studies of VO2 films have been carried out, the reliability of VO2 films that undergo thermal cycling has not been extensively studied. In this investigation, a framework for testing this thermal cycling reliability of vanadium dioxide (VO2) films was created. The text fixture is comprised of several major components, including a wafer with VO2 films and integrated Joule heater elements, a test controller board for generating configurable PWM waveforms for the heater elements, a mount to secure the board and the wafer together, and software to manage and monitor the thermal reliability study. Simulations were performed using COMSOL Multiphysics simulator to determine the necessary parameters of the heating signal voltage and current that are required to thermally cycle the VO2 films. The controller board was then designed to be able to provide such a signal, and a printed circuit board (PCB) was created using KiCad. The board was manufactured and assembled, and custom firmware was loaded onto the microcontroller chip to enable communication with a host computer over a USB interface. After establishing the physical dimensions of the controller board, a mount was designed to securely hold the controller board and wafer in contact with each other using spring- loaded pins. Finally, a Python script was developed to operate the controller board from a host computer, including reading out data from the board. Due to the COVID-19 pandemic, wafer manufacturing was significantly delayed, but the functionalities of the test system were verified using a resistor as a simulated load. The board performed to the specifications set by the simulations and was able to output a configurable 16V PWM signal. The framework for testing thermal cycling reliability developed in this project will be applied to understanding the thermal reliability of vanadium dioxide films, but it can also be easily extended to other reliability studies that involve voltage, current, or thermal activation of the device under test.
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Keywords
Vanadium dioxide, thermal reliability, phase change material, switching devices