Simulation and Fabrication of Inkjet-Printed mm-Sized Capacitors for Wearable Temperature Sensing Applications

Wireless detection of temperature with passive components offers a wide variety of applications from healthcare monitoring to industrial. A passive resonant device with a temperature-sensitive dielectric layer has a specific resonant frequency. The dielectric permittivity of the layer changes with the changes in temperature. This dielectric shift causes a change in the capacitance, and therefore the resonant frequency. This frequency shift can be used to calculate the temperature of the ambient environment. A capacitor with a temperature-sensitive dielectric and an inductor in parallel are sufficient to form such a temperature sensor. This work explores the design, simulation, and fabrication of capacitors for resonant-based sensors. The designs include parallel-plate capacitors and interdigitated capacitors, both of which use 6 μm hexagonal boron nitride (h-BN) as the dielectric layer. The devices are first simulated and modeled in Ansys high-frequency structure simulator (HFSS). The S-parameters and Z-parameters are analyzed to calculate the capacitance. The designs are inkjet-printed with silver ink on silicon dioxide wafers. Inkjet-printing is a quick and cost-effective method for both prototyping and mass production of circuits. These capacitors are intended for later use in conjunction with inkjet-printed inductors for the development of resonant temperature sensors on polyimide.