A novel technique for fabrication of MEMS based capacitive pressure sensor using press-on-contact in anodic bonding

Abstract

A novel technique for fabrication of capacitive pressure sensor was conceived and implemented using press-on-contact in silicon-to-glass anodic bonding process. The novelty of the design lies in using a glass plate (Corning®7740) having through holes and metallization pattern for anodic bonding process. This enables the formation of press-on-contact between metal patterns on Si-sensor wafer and the glass plate. Silicon-to-glass bonding was carried out at wafer level and individual chips were separated by dicing technique. This methodology enables batch fabrication of the sensor chip wherein the bonding is done at wafer level for all the chips before separating the individual chips by dicing. For this purpose, press-on-contact in anodic bonding process was studied in detail to be used in fabrication of capacitive pressure sensor. The electrical continuity and the contact resistance of patterned metal were measured experimentally. The capacitive pressure sensor was fabricated using the proposed technique. The sensing element was a recessed silicon diaphragm of 5 μm thickness which was formed by anisotropie etching of silicon in 40 wt.% KOH solution using boron diffusion as etch stop layer for precise control of diaphragm thickness. After fabrication of capacitive pressure sensor, the change in capacitance was measured with applied pressure. The sensitivity was found to be ∼ 1 pF / kg-cm−2 over the pressure range 0 to 0.6 kg/cm2. Thus, a capacitive pressure sensor using novel scheme was designed, simulated, fabricated and tested as proof-of-concept.