It has no temperature compensation, has low sensitivity, and rather low yield. This increases linearity of the capacitor by ensuring that the capacitive plates, which are situated over the boss, are flat and move without bending relative to the top plate. The top plate is formed on Pyrex glass etched to form support columns to hold the capacitor top plate at the proper distance from the bottom. The metal top plate is deposited directly onto the glass, and the glass structure is bonded anodically to the chip. Chip circuitry features a programmable voltage reference and a switched-cap amplifier.
Output is a voltage, which makes it easier to compare the performance to that of our chip.
The standard CMOS process involves about 7 or 8 mask steps, and the chip requires one additional mask to define the bossed membrane, and two mask steps are required to etch and metallize the Pyrex glass. This is a total of at least 10 masks for fabrication, compared to our four masks. 500 Pa. The capacitor pressure sensor therefore has an operating range which is orders of magnitude larger than that of our chip. Sensitivity for the capacitive sensor is measured as change in capacitance per unit pressure. The capacitor has temperature-dependent offsets and sensitivity which, although not as severe as temperature dependencies in a resistor, can be reduced by the bandgap reference circuit.