Effect of Substrate-Thickness on Voltage Responsivity of MEMS-Based ZnO Pyroelectric Infrared Sensors

Chia-Yen Lee,Cheng-Xue Yu,Kuan-Yu Lin,Lung-Ming Fu

doi:10.3390/app11199074

Abstract

Pyroelectric infrared sensors incorporating suspended zinc oxide (ZnO) pyroelectric films and thermally insulated silicon substrates are fabricated using conventional MEMS-based thin-film deposition, photolithography, and etching techniques. The responsivity of the pyroelectric films is improved through annealing at a temperature of 500 °C for 4 h. The temperature variation and voltage responsivity of the fabricated sensors are evaluated numerically and experimentally for substrate thickness in the range of 1 to 500 μm. The results show that the temperature variation and voltage responsivity both increase with a reducing substrate thickness. For the lowest film thickness of 1 μm, the sensor achieves a voltage sensitivity of 3880 mV/mW at a cutoff frequency of 400 Hz. In general, the results presented in this study provide a useful source of reference for the further development of MEMS-based pyroelectric infrared sensors.

Highlights

For the pyroelectric sensor considered in the present study, the output voltage scales proportionally with the temperature variation within the zinc oxide (ZnO) layer
The results show that the rate of change of the temperature at point A1 increases with a decreasing substrate thickness
For all of the sensors, the output voltage reduces to zero as the sensing distance increases beyond 100 cm

Summary

Introduction

The device was characterized over a modulation frequency range of 0.2 to 10 Hz and was found to have a voltage sensitivity of 191 mV/mW at a modulation frequency of 1 Hz when implemented with a 500 μm thick silicon substrate. The sensor response was enhanced by depositing the sensing elements on a thermally isolated and freestanding Si3 N4 /SiO2 membrane created by removing the underside of the SiO2 substrate using a conventional back-etching technique. The experimental results showed that the device achieved a maximum voltage sensitivity of. The present study fabricates pyroelectric sensors consisting of suspended zinc oxide (ZnO) pyroelectric films with substrate thicknesses ranging from 1 to 500 μm supported on thermally insulated backetched silicon substrates. The results show that the performance of the proposed sensor improves as the thickness of the substrate reduces

Principles and Designs

Simulation Method

Fabrication

Results and Discussion

Conclusions