Micromachined differential pressure transducers and method of producing the same

Claim 1

A micromachined differential pressure transducer comprising: (a) a substrate having top and bottom sides; (b) a deformable membrane mounted to and sealed at its peripheral edges to the top of the substrate and spaced from the substrate at its central portion to define a cavity which is sealed between the membrane and the substrate, the bottom of the cavity in the substrate being spaced from the membrane to allow normal deflections of the membrane but providing an overpressure stop for membrane deflection toward the substrate to prevent damage to the membrane; (c) at least one channel leading from a remote position in the substrate to the cavity to provide communication therefrom to the cavity; (d) an overpressure stop mounted to the top of the substrate and having a bridge portion spanning the membrane and spaced therefrom to allow normal deflections of the membrane while providing an overpressure stop to prevent displacements of the membrane away from the substrate which would damage the membrane, the spacing between the overpressure stop bridge and the membrane and between the membrane and the bottom of the cavity being less than about 10 micrometers; and (e) means for sensing the deflections of the membrane.

Claim 14

A method of making a micromachined differential pressure transducer comprising the steps of: (a) forming a deformable polysilicon membrane over a cavity between the membrane and a substrate, the membrane being sealed to the top side of the substrate at peripheral portions of the membrane to seal off the top surface of the membrane from the cavity; (b) forming at least one channel in the substrate or membrane extending from a position remote to the cavity into communication with the cavity; (c) forming a spacer release layer of hardenable material over the membrane and adjacent to the surface of the membrane which can be dissolved in a liquid which does not affect the diaphragm or the substrate; (d) applying a plating base over the spacer release layer and adjacent substrate, the plating base being formed of a metal; (e) forming a layer of casting material over the plating base to at least the desired thickness of an overpressure stop bridge which is to span over the deformable membrane, the deposited casting material being susceptible to X-rays such that the material exposed to X-rays can be dissolved in a selected solvent; (f) exposing the casting material to X-rays in a desired pattern around and including the area of the deformable membrane; (g) removing the casting material with the solvent in those areas which have been exposed to X-rays while leaving the remaining casting material to define a mold area over the diaphragm and surrounding areas; (h) depositing a solid metal into the mold area; (i) removing the remaining casting material; (j) removing the spacer release layer material to leave the deposited metal as a bridge extending across the space above the deformable membrane.

Claim 17

A method of making a micromachined structure comprising the steps of: (a) forming a sacrificial release layer of material on the surface of a substrate, the material of the sacrificial release layer being dissolvable in a liquid which does not affect the substrate; (b) applying a plating base at least over the sacrificial release layer, the plating base being formed of a metal; (c) forming a layer of casting material over the plating base to at least the desired thickness of a structure to be formed, the deposited casting material being susceptible to X-rays such that the casting material exposed to X-rays can be dissolved in a selected developer solvent; (d) exposing the casting material to X-rays in a desired pattern including at least a part of the area of the plating base; (e) removing the casting material with the developer solvent in those areas which have been exposed to X-rays while leaving the remaining casting material to define a mold area over the plating base; (f) depositing a solid metal into the mold area onto the plating base by electroplating; (g) removing the remaining casting material; (h) removing the plating base in regions where solid metal has not been deposited to allow access to the sacrificial release layer; (i) removing the sacrificial release layer material to leave the deposited metal on the plating base free of the substrate where the sacrificial release layer has been removed.

Claim 19

The method of any one of claims 14 to 18, wherein the sacrificial release layer is formed of polyimide.

Claim 20

The method of any one of claims 14 to 19, wherein the plating base includes a thin layer of titanium and a thin layer of nickel.

Claim 21

The method of any one of claims 14 to 20, wherein the casting material is polymethyl methacrylate, preferably cross-linked polymethyl methacrylate.

Claim 22

The method of any one of claims 14 to 21, wherein the metal which is plated is nickel.

Claim 23

The method of any one of claims 14 to 22, wherein the release layer is deposited to a thickness of 10 micrometers or less.

Claim 25

The method of any one of claims 14 to 24, wherein the step of exposing the casting material to X-rays is carried out by exposing the casting material to synchrontron radiation.