We have developed the high accuracy and high reliability semiconductor pressure sensor for measuring intake manifold pressure and atmospheric pressure. Its heart is composed of a 3 × 3 mm silicon diaphragm chip, four piezoresistors being diffused and connected to a Wheatstone bridge. Hereupon, the silicon crystal plane, axis, diaphragm configuration, and piezoresistor positions are optimumly designed, being based on the stress analysis of the diaphragm. It features the selection of the octagonal diaphragm and not the round or square one used in general. Its output is around 50 mV/80 kPa and is affected by ambient temperature. So, it was not only amplified, but temperature compensated for by the unique hybrid IC circuit with thermistors. As a result, we have realized temperature characteristics within a ±1.5% error of F.S. (80 kPa) at 0°C ~ +85°C and ±3% F.S. at −40°C ~ +125°C.
On the other hand, we conducted various kinds of durability tests in operating conditions including pressure and temperature cycling of −85 kPa ↔ +100 kPa, −40°C ↔ +130°C, humidity of 85°C, 85% RH, liquid, vibration, and as a result the reliability has been proven to be satisfactory for automobiles. Moreover, it features this sensor being protected from EMI (Electro-Magnetic Interference).
Our differential pressure sensor is applied to indicate the manifold pressure, installed in a turbocharged car. An MAP sensor is used for the microcomputer controlled ignition system. In this case, a sensor is small enough, so that it is contained in the control unit, and a barometric pressure sensor for altitude compensation is mounted on a printed circuit board.