Application of Nondestructive Techniques to Investigate Dissolvable Amorphous Metal Tungsten Nitride for Transient Electronics and Devices

Abstract

Transient electronics can be gradually dissolved in a variety of liquids over time. The short-lived nature of such electronics has promoted their implementation in prospective applications, such as implantable electronics, dissolvable devices for secure systems, and environmentally biodegradable electronics. The amorphous metal tungsten nitride (WNx) has the remarkable ability to scale down to the nano-scale, allowing the fabrication of sub-1 volt nano-electromechanical (NEM) switches. When compared to silicon, amorphous WNx has a greater density and electrical conductivity, making it an even more appealing material for the design of accelerometers and resistive temperature detectors. Kinetic hydrolysis is observed by the dissolution of amorphous WNx in ground water. To better understand the kinetics of hydrolysis, in this paper, samples are dissolved in different solutions under different conditions over time. NEM switches immersed in ground water, de-ionized (DI) water, and salty water are subjected to temperatures of 0 °C (degrees Celsius), 25 °C (room temperature, RT), and 60 °C. Sonicated samples are tested at both room temperature (RT) and at 60 °C. During the course of dissolving, the resistivity of amorphous WNx is measured, and an increase in resistance is noted when the thickness of the amorphous WNx is reduced. The wettability of a solid can be easily determined by measuring its contact angle, which indicates either the hydrophobic or hydrophilic nature of the surface. The contact angle of the amorphous WNx is measured to be about 30.8°, indicating hydrophilicity. For the temperature sensor characterization, a probe station with a thermal chuck is used to apply heat from the bottom of the sensor. The actual real-time temperature of the amorphous WNx sensor is measured using a thermocouple tip on the surface of the sensor.