Sensor having a membrane

Details Sensor having a membrane Sensor having a membrane

1998-10-06

2001-06-05

Patel, Harshad (Department: 2855)

Measuring and testing

Volume or rate of flow

Thermal type

C073S204110

Reexamination Certificate

active

06240777

ABSTRACT:

BACKGROUND INFORMATION
International Patent Publication No. WO 89/05963 describes a mass flow sensor having a membrane. The membrane is composed of a multiplicity of dielectric layers. On the membrane, thin-film resistor elements are arranged which are used to heat the membrane and to measure the temperature of the membrane. The membrane is composed of a plurality of layers which are selected with regard to their thermal expansion coefficients such that slight tensile stresses relative to the silicon frame are enabled to be set. On the upper side of the membrane and of the resistor elements, a covering layer is applied, also made of a dielectric material.
SUMMARY OF THE INVENTION
A sensor according to the present invention has the advantage that, as a result of a covering layer which also has slight tensile stresses in itself, the stability of the membrane is improved.
As a result of the multi-layer construction of the covering layer, the possibilities for adjusting the stress conditions in the covering layer are improved. Furthermore, because of the multi-layer design, the standards of the covering layer, in particular concerning its adhesion and the seal tightness, can be raised. Through the use of a first partial layer, having a certain silicon residue, particularly good adhesion to the resistor elements, made from a thin film, can be attained. Through a stoichiometric silicon layer, applied thereon, particularly good protection against humidity is achieved. Moreover, a first partial layer of silicon oxide and on top of that a second partial layer of silicon oxide, silicon nitride or a combination having tensile stresses can be used. It is also advantageous to provide a symmetrical construction, in which the tensile stress of the membrane is roughly equal to the tensile stresses in the covering layer, since in this way a stress gradient in the individual layers is reduced and a rupture of the layers is prevented. The layers can also seamlessly pass over into each other.


REFERENCES:
patent: 5393351 (1995-02-01), Kinard et al.
patent: 5428244 (1995-06-01), Segawa et al.
patent: 5627403 (1997-05-01), Bacchetta et al.
patent: 5659127 (1997-08-01), Shie et al.
patent: 5804462 (1998-09-01), Liu et al.
patent: 5815223 (1998-09-01), Watanabe et al.
patent: 37 11 511 (1988-06-01), None

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