Semiconductor pressure transducer employing temperature compensation circuits and novel heater circuitry

Claim 1

A semiconductor pressure transducer apparatus comprising a semiconductor body comprising a substrate and a surface layer of a material of a first conductivity type, said body having a cavity region formed therein, said cavity region including a thin wall section formed by a section of said surface layer, said thin wall section being flexible responsive to pressure exerted across said thin wall section, an electrical bridge circuit formed in said thin wall section of said surface layer and comprising four resistor arms, two opposed nodes of said bridge forming a bridge input, the two other opposed nodes of said bridge forming a bridge output, each of said bridge resistors being formed by a diffusion of a dopant of opposite conductivity type to that of the surface layer into said thin semiconductor wall section, circuit means for applying a voltage to the input nodes of said bridge circuit, said circuit means including a common collector node formed by said layer of said semiconductor material of said first conductivity type, a Zener diode formed in said surface layer comprising an emitter, a collector coupled to said common collector node, and a base coupled to one input node of said bridge, a temperature compensation circuit for said Zener diode comprising a first transistor formed in said surface layer having an emitter coupled to the emitter of said Zener diode, a base, and a collector coupled to said common collector node, and a pair of resistors coupled in series between said common collector node and the emitter of said first transistor, the junction node between said two resistors being coupled to the base of said first transistor, a temperature compensation circuit coupled between another input node of said bridge and said common collector node comprising a second transistor formed in said surface layer having an emitter coupled to said other bridge input noDe, a collector coupled to said common collector node, and a base, and a pair of resistors coupled in series between said common collector node and the emitter of said second transistor, the junction node between said two resistors being coupled to the base of said second transistor, and a heating circuit thermally well coupled to the piezoresistor bridge for heating the thin wall section for the cavity region comprising a transistor formed in said thin wall section comprising a base region diffused in said surface layer, an emitter diffused in said base region, and a collector region common to said common collector node, said base and emitter region having output leads to which energy pulses may be applied to heat the thin semiconductor wall section.