Gas flow sensor and method of producing a gas flow sensor

Abstract

A mass gas flow sensor for measuring the mass flow rate of a gas through a passage, and a method of manufacture thereof. The sensor includes a substrate having a streamlined end surface which is to project upstream in the passage, upstream and downstream heating resistors formed on the substrate, protective films covering the resistors, and circuitry for applying current to the resistors so as to heat the resistors, the gas cooling the upstream resistor more than the downstream resistor. The circuitry also produces an electrical voltage responsive to differences in voltage across the upstream and downstream resistors, corresponding to the mass gas flow in the passage. In a mass production method of manufacture of a preferred embodiment, a composite substrate material is produced with hollow portions therein by joining a first integral wafer having a plurality of grooves with a second integral wafer which closes the grooves, and providing a plurality of resistors on the composite substrate material by photolithography and etching directly over the grooves before cutting the substrate material into a plurality of hollow substrates. One end surface of each of the hollow substrates is then tapered to provide a streamlined shape.