Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
2001-05-25
2004-02-10
Hirshfeld, Andrew H. (Department: 2854)
Measuring and testing
Fluid pressure gauge
Diaphragm
C073S716000, C073S717000, C073S718000, C361S283400
Reexamination Certificate
active
06688181
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a membrane pressure sensor containing silicon carbide. It also concerns the manufacture of the sensing element of the sensor.
PRIOR ART
With micro-electronic techniques it is possible to produce miniature pressure sensors using collective manufacturing processes. Small-sized sensors can therefore be produced at low cost. They provide the possibility of producing a sensor and its associated electronics on one same carrier.
Micro-machined pressure sensors are known, made up of a silicon membrane a few tenths of a &mgr;m in thickness. The difference in pressure between the two surfaces of the membrane may be detected by measuring the recess stresses by means of piezoresistive gauges obtained by ion diffusion or implantation. These piezoelectric gauges have high sensitivity and extensive mechanical stability due to the monocrystalline structure of the silicon used. Between each gauge and the substrate on which they are fabricated, electric insulation is achieved using reverse junctions. This has the disadvantage of limiting the range of operating temperature of these sensors to a maximum of 125° C. due to the strong leakage current at the reverse junction, and of causing a high noise level (thermal noise and piezoelectric junction noise) which reduces the dynamic range. A further disadvantage of piezoresistive gauges for their usual use results from the direct exposure of these gauges and from metallisation related to the fluid whose pressure is to be measured, which submits these elements to the effects of humidity and corrosive agents.
Pressure sensors are also known with piezoresistive gauges embedded in the silicon. However, these sensors cannot be used for temperatures over 200° C.
Pressure sensors made on SOI (Silicon-On-Insulator) substrates are also known. These sensors do not have the disadvantages due to leakage current or to noise on account of the intermediate insulating layer. They may be used up to temperatures in the order of 400° C.
Research is currently focusing on techniques using silicon carbide, which are able to provide products able to operate up to temperatures in the order of 700°C.
These micro-machined pressure sensors are encapsulated in relation to their intended use. Pressure sensors for the automotive industry and those intended to be mounted on a board are generally encapsulated in pre-moulded “dual-in-line” type casings. Some casings may be custom-made in relation to the intended application, by designing a pre-moulded housing in thermoplastic material to ensure the best possible mechanical integration of the sensor, and by using the “dual chip” technique for the incorporation of associated electronics. In practice, this type of encapsulation offers very few application possibilities and the presence of thermoplastic material imposes a maximum temperature.
The use of pressure sensors in a hostile environment requires giving consideration to the restraints of temperature, and the type of fluid whose pressure it is sought to measure, in particular its corrosive nature. So as to protect the membrane of the sensor from its immediate environment, encapsulation frequently integrates means for the hydraulic transmission of the pressure to be measured, combining for example silicon oil and a membrane or a metal bellow device. This solution has the disadvantage of increasing the cost of the sensor. Also, silicon oil does not withstand a temperature greater than 300° C. For higher temperatures, mercury may be used, but regard must be given to its harmful effect on the environment.
In a hostile medium, encapsulation may further use materials such as stainless steel and ceramic in order to protect the silicon part of the sensor. The sensor membrane may be protected from the medium, whose pressure is to be measured, by another membrane which directly covers the first membrane (enabling operation of the sensor up to 300° C.) or by a mechanical pressure transmission system using a diaphragm (which enables operation of the sensor up to 450° C).
U.S. Pat. No.4,898,035 discloses a ceramic pressure sensor, for the measurement in particular of the pressure in the cylinder of an internal combustion engine. This sensor comprises a sensing element integrating a membrane, a first surface of the membrane being intended to contact the medium whose pressure is to be measured. The second surface of the membrane supports membrane deformation detection means connected to electric conductors, not shown. The membrane being is ceramic, its surface intended to contact the hostile medium is chemically inert relative to this medium. The carrier of the sensing element supports this element so that one of the surfaces of the membrane is in contact with the hostile medium and the opposite surface is shielded from this contact. The carrier and ring disk are metallic. The seal between the inside of the sensing element and its carrier is ensured by the connection layer in glass or a brazing material.
U.S. Pat. No. 4,894,635 discloses a stress sensor, for example a pressure sensor. This sensor is intended to operate at high temperature. It is also intended for use in a hostile medium such as vehicle engines. The sensing element is formed from a substrate in ceramic. It comprises a membrane of which one surface is exposed to the medium whose pressure is to be measured, and the other surface supports the detection means. Parts act as support for the sensing element. They place one of the membrane surfaces in contact with said medium and prevent the surface opposite the membrane from coming into contact with this medium. The seal is ensured by a toroidal joint.
Document DE-A-196 01 791 discloses a membrane detector and its method of manufacture. The detector is a micro-machined structure comprising a deformable membrane integral with a peripheral part enabling its deformation. The membrane comprises a layer in SiC and a layer in SiO2. The detection elements are placed on the electric insulating layer.
U.S. Pat. No. 4,706,100 discloses a piezoresistive pressure sensor comprising: a substrate of monocrystalline silicon, an epitaxied layer of monocrystalline □-SiC, piezoelectric resistances formed by diffusion or implantation in the epitaxied layer, electric contacts to connect the piezoelectric resistances and a cavity formed on the rear surface of the substrate to form a membrane.
DESCRIPTION OF THE INVENTION
The present invention was designed to remedy the disadvantages of pressure sensors of the prior art. It can be used to produce a miniature pressure sensor manufactured by collective manufacturing processes, compatible with resistance to a severe environment (high temperature, chemically aggressive measuring medium), compatible with simplified encapsulation and having a low production cost.
The subject of the invention is therefore a pressure sensor able to operate at high temperature and to measure the pressure of a hostile medium, comprising:
a sensing element integrating a membrane in monocrystalline silicon carbide and produced by micro-machining a substrate in polycrystalline silicon carbide, a first surface of the membrane being intended to be placed in contact with said medium, a second surface of the membrane comprising means to detect membrane deformation connected to electric contacts for connection of the electric connection means, the surfaces of the sensing element intended to be in contact with said medium being chemically inert relative to this medium;
a carrier supporting the sensing element so that said first surface of the membrane may be contacted with said medium and the second surface of the membrane may be shielded from contact with said medium, the carrier being in polycrystalline silicon carbide;
a seal strip in material containing silicon carbide brazed between the carrier and the sensing element to protect the second surface of the membrane against any contact with said medium.
If the sensor is intended to measure absolute pressure, the carrier may comprise a sealed closing part so that a vacuum can be set up i
Clerc Jean-Frederic
Jaussaud Claude
Joly Jean-Pierre
Therme Jean
Commissariat a l'Energie Atomique
Ferguson Marissa
Hirshfeld Andrew H.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Membrane pressure sensor comprising silicon carbide and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Membrane pressure sensor comprising silicon carbide and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Membrane pressure sensor comprising silicon carbide and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3282494