| 摘要 |
PROBLEM TO BE SOLVED: To provide a thermal gas flow sensor capable of reducing changes over time in resistance values of a heating resistor and a temperature measuring resistor and improving detection accuracy. SOLUTION: In a detection element 1, protective films 30a, 30b and 31a: insulating films 31b and 30c; the heating resistor 3; the temperature measuring resistor 4; etc. are formed in a flat substrate 32 constituted of a material having high thermal conductivity. The flat substrate 32 is etched from its back surface to form a lower space 35 at a lower part of the insulating film 30c and form a diaphragm 2. Since the membrane stress of the diaphragm 2 varies due to the desorption of H<SB>2</SB>O from the uppermost-surface protective film 30a when the heating resistor is heated to vary a resistance value of the heating resistor 3 due to the piezoresistance effect, the protective film 30a is made of an oxynitride film (an SiON film) and a polysilicon film of a nonadsorbing material which contains only a small content of H<SB>2</SB>O. It is thereby possible to reduce contents of H<SB>2</SB>O and others, the occurrence of cracks, and variations in resistance values of the heating resistor and the temperature measuring resistor. COPYRIGHT: (C)2008,JPO&INPIT
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