A high-Q resonant pressure microsensor with through-glass electrical interconnections based on wafer-level MEMS vacuum packaging.

Zhenyu Luo,Junbo Wang,Jian Chen,Yinan Li,Deyong Chen

doi:10.3390/s141224244

Abstract

This paper presents a high-Q resonant pressure microsensor with through-glass electrical interconnections based on wafer-level MEMS vacuum packaging. An approach to maintaining high-vacuum conditions by integrating the MEMS fabrication process with getter material preparation is presented in this paper. In this device, the pressure under measurement causes a deflection of a pressure-sensitive silicon square diaphragm, which is further translated to stress build up in “H” type doubly-clamped micro resonant beams, leading to a resonance frequency shift. The device geometries were optimized using FEM simulation and a 4-inch SOI wafer was used for device fabrication, which required only three photolithographic steps. In the device fabrication, a non-evaporable metal thin film as the getter material was sputtered on a Pyrex 7740 glass wafer, which was then anodically bonded to the patterned SOI wafer for vacuum packaging. Through-glass via holes predefined in the glass wafer functioned as the electrical interconnections between the patterned SOI wafer and the surrounding electrical components. Experimental results recorded that the Q-factor of the resonant beam was beyond 22,000, with a differential sensitivity of 89.86 Hz/kPa, a device resolution of 10 Pa and a nonlinearity of 0.02% F.S with the pressure varying from 50 kPa to 100 kPa. In addition, the temperature drift coefficient was less than −0.01% F.S/°C in the range of −40 °C to 70 °C, the long-term stability error was quantified as 0.01% F.S over a 5-month period and the accuracy of the microsensor was better than 0.01% F.S.

Highlights

High-accuracy barometric pressure microsensors have been the subject of extensive research due to their applications in the fields of aerospace exploration, atmospheric pressure monitoring, etc. [1].Depending on the detection mechanisms, these microsensors can be classified into capacitive pressure sensors [2,3], piezoelectric pressure sensors [4,5], piezoresistive pressure sensors [6,7] and resonant pressure sensors [8]
For MEMS-based pressure sensors, the vacuum packaging is different from the conventional packaging counterparts based on ceramic or metal hermetic sealing, which can lead to compromise of the MEMS devices during the manufacturing process due to their movable and fragile structures
Through-glass vias [23,24] and silicon-to-glass anodic bonding technologies were utilized in this study to fabricate a resonant pressure sensor consisting of an SOI wafer and a

Summary

Introduction

High-accuracy barometric pressure microsensors have been the subject of extensive research due to their applications in the fields of aerospace exploration, atmospheric pressure monitoring, etc. [1]. A variety of bonding techniques have been proposed for wafer-level vacuum packaging, such as intermediate layer bonding, silicon–silicon fusion bonding, and silicon–glass anodic bonding [18] Among these approaches, the electrical interconnections between the bonding micro-cap and the device substrate pose several challenges for vacuum packaging. Limited by the physical properties of organic materials, the poor long-term vacuum tightness is its fatal defect To address these issues, through-glass vias [23,24] and silicon-to-glass anodic bonding technologies were utilized in this study to fabricate a resonant pressure sensor consisting of an SOI wafer and a. (a) Previous work based on low-temperature adhesive bonding with patterned electrodes across the bonding interface; (b) New design presented in this paper with SOI-glass anodic bonding and through-glass via holes, which provide electrical interconnections with the outside. The vias provide electrical signal paths to the pressure device

Device Design

FEM Simulation

Device Fabrication

Device Characterization

Findings

Conclusions