This paper proposed a new direction for the miniaturization of silicon bulk-machined sensors. Herein, the glass substrate bonded with the silicon wafer replaces the role of the silicon wafer. Then the whole silicon wafer with sensing portions, whatever piezo-resistive or capacitive types, could be all machined to the membrane structure without chip-area wasting on the {111} surfaces. Basically, the chip size by this semi-SOI method would be as small as the surface-machined one in principle, if the silicon-glass bonding process is guaranteed. The other advantages of this strategy include the process compatibility with the different sensing principles and the different techniques of membrane machining. The on-chip circuitry of sensors could be also preserved. Another important issue is that the surface-machining-like membrane now is mono-crystalline, which means the stable mechanical properties and reproducible characteristics. This new strategy practically augmented the mass production of piezoresistive pressure sensors. The 1.0mm X 0.8mm X 0.5mm of sensor size with chip density exceeds 5,000 per 4-inch wafer was successfully fabricated.
