Thermal Air Flow Sensor

Abstract

A thermal air flow sensor that produces less measurement error is provided. The thermal air flow sensor includes: a semiconductor substrate; a heating resistor, resistance temperature detectors, and an electrical insulator that includes a silicon oxide film, wherein the heating resistor, the resistance temperature detectors, and the electrical insulator are formed on the semiconductor substrate; and a diaphragm portion formed by removing a portion of the semiconductor substrate. The heating resistor and the resistance temperature detectors are formed on the diaphragm portion. The thermal air flow sensor further includes a silicon nitride film formed as the electrical insulator above the heating resistor and the resistance temperature detectors. The silicon nitride film has steps conforming to the patterns of the heating resistor and the resistance temperature detectors. The silicon nitride film has a multilayer structure.

1 . A thermal air flow sensor comprising:
 a semiconductor substrate;   a heating resistor, resistance temperature detectors, and an electrical insulator that includes a silicon oxide film, wherein the heating resistor, the resistance temperature detectors, and the electrical insulator are formed on the semiconductor substrate; and   the heating resistor and the resistance temperature detectors being formed on a diaphragm portion of the semiconductor substrate;   the silicon oxide film formed as the electrical insulator being disposed on the heating resistor and the resistance temperature detectors;   the thermal air flow sensor further comprising a silicon nitride film laminated on the silicon oxide film;   wherein steps are arranged on the silicon oxide film, and the steps correspond to patterns of the heating resistor and the resistance temperature detectors; and   wherein a thickness of the silicon oxide film where the heating resistor and the resistance temperature detectors are disposed is smaller than a thickness of the silicon oxide film where the heating resistor and the resistance temperature detectors are not disposed.   
     
     
         2 . The thermal air flow sensor according to  claim 1 , wherein heights of the steps are smaller than heights of the heating resistor and the resistance temperature detectors. 
     
     
         3 . The thermal air flow sensor according to  claim 1 , wherein the silicon nitride film comprises plural layers. 
     
     
         4 . The thermal air flow sensor according to  claim 1 , wherein a hillock is formed on the heating resistor and the resistance temperature detectors.