Heterogeneous sensors of pressure sensor and ultraviolet photodetector fabricated by vertical 3D stacking as a multi-functional device

Abstract

Microelectromechanical system (MEMS) piezoresistive pressure sensor and ZnO nanowires (NWs) ultraviolet (UV) photodetector were 3D integrated into a single chip with a vertically stacked structure. The MEMS pressure sensor with a UV transparent SiO₂ diaphragm was stacked on the top of UV photodetector. The fabricated pressure sensor presents good linearity and stability with increasing applied pressure from 0–500 mbar. The measured interval of 0.2 mbar also shows its high sensitivity with a small change in pressure and altitude. For the ZnO NWs UV photodetector, the cutoff wavelength was around 360 nm, and the measured responsivity was 6.2 × 10⁻¹ A W⁻¹ with 5 V applied bias. To discuss the influence of the applied pressure and UV on this 3D stacked device, the pressure sensor was also measured with and without UV illumination, and the UV photodetector was measured at various applied pressures. The results show that UV variation can be ignored for pressure sensor measurement. However, the photoresponses of ZnO NWs decreased, whereas the applied pressure was increased.