Silicon based mass airflow sensor and its fabrication method
First Claim
Patent Images
1. A mass airflow sensor having a longitudinal axis comprising:
- a dielectric diaphragm;
a thin-film heating element disposed on said diaphragm;
a thermally conductive semiconductor rim comprising a heavily doped etch stopped region encompassing at least a major portion of said dielectric diaphragm; and
at least one thin-film sensing element disposed on said diaphragm, said at least one sensing element being disposed at least in part over said semiconductor rim, whereby the temperature gradient between the heating element and said at least one sensing element may be monitored to determine the airflow rate, said heating element being centrally disposed substantially along the longitudinal axis of the sensor and a plurality of sensing elements disposed on both sides of said heating element.
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Abstract
A mass airflow sensor is fabricated on a semiconductor substrate and which includes (1) a dielectric diaphragm, (2) p-etch-stopped silicon rim, (3) thin-film heating and temperature sensing elements, and (4) tapered chip edges. The dielectric diaphragm is formed with thin silicon oxide and silicon nitride in a sandwich structure and provides excellent thermal insulation for the sensing and heating elements of the sensor. The diaphragm dimensions, including thickness, are accurately controlled through the use of the heavily-p-doped silicon rim to help ensure uniform and reproducible sensor performance.
89 Citations
43 Claims
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1. A mass airflow sensor having a longitudinal axis comprising:
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a dielectric diaphragm; a thin-film heating element disposed on said diaphragm; a thermally conductive semiconductor rim comprising a heavily doped etch stopped region encompassing at least a major portion of said dielectric diaphragm; and at least one thin-film sensing element disposed on said diaphragm, said at least one sensing element being disposed at least in part over said semiconductor rim, whereby the temperature gradient between the heating element and said at least one sensing element may be monitored to determine the airflow rate, said heating element being centrally disposed substantially along the longitudinal axis of the sensor and a plurality of sensing elements disposed on both sides of said heating element. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A mass airflow sensor comprising:
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a dielectric diaphragm; a thin-film heating element disposed on said diaphragm; a thermally conductive semiconductor rim encompassing at least a major portion of said dielectric diaphragm and comprised of p-etch-stopped silicon; and at least one thin-film sensing element disposed on said diaphragm, the diaphragm dimensions being determined by the semiconductor rim. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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25. A mass airflow sensor fabricated on a semiconductor substrate comprising:
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a dielectric diaphragm; a heating element and at least one temperature sensing element disposed on said diaphragm; a semiconductor region disposed adjacent said diaphragm; at least one temperature sensing element disposed over said semiconductor region, whereby an airflow therepast may be determined based on the temperature gradient between the heating element and said at least one temperature sensing element disposed over said semiconductor region, said semiconductor region comprising a heavily doped etch stopped region which surrounds said dielectric diaphragm. - View Dependent Claims (26, 27, 28, 29, 30, 31, 32, 33, 34)
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35. A mass airflow sensor having a longitudinal axis comprising:
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a dielectric diaphragm; a thin-film heating element disposed on said diaphragm; a thermally conductive semiconductor rim encompassing at least a major portion of said dielectric diaphragm; at least one thin-film sensing element disposed on said diaphragm, said at least one sensing element being disposed at least in part over said semiconductor rim, whereby the temperature gradient between the heating element and said at least one sensing element may be monitored to determine the airflow rate, said heating element being centrally disposed substantially along the longitudinal axis of the sensor and a plurality of sensing elements disposed on both sides of said heating element; and said dielectric diaphragm having a sandwich structure of dielectric materials having substantially different coefficients of thermal expansion, said sandwich structure being comprised of silicon dioxide and silicon nitride. - View Dependent Claims (36, 37, 38, 39, 40, 41, 42, 43)
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Specification