Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
1998-06-17
2001-12-11
Oen, William (Department: 2855)
Measuring and testing
Fluid pressure gauge
Diaphragm
Reexamination Certificate
active
06327911
ABSTRACT:
FIELD OF INVENTION
This invention relates generally to semiconductor microsensor structures and more specifically, to high temperature semiconductor pressure transducers fabricated from beta-silicon carbide.
BACKGROUND OF THE INVENTION
Prior art high temperature semiconductor pressure transducers are typically made by adhesively bonding the sensing elements to a metal diaphragm or by diffusing the sensing elements into a silicon diaphragm. The devices which employ metal diaphragms generally have high temperature capability, however, the metal diaphragms have gage factors of approximately 1-2. The silicon diaphragms of the other devices exhibit a relatively large gage factor up to approximately 400° C., however, the silicon diaphragms cannot handle any significant loads at temperatures above approximately 500° C.
Higher temperature operation of pressure transducers employing silicon diaphragms has been made possible by providing a dielectric isolation between the silicon sensor network and the silicon diaphragm-like force collector. These devices are generally capable of operating at temperatures in excess of 500° C. Above 600° C., however, the silicon sensing network as well as the silicon diaphragm, undergo significant plastic deformation rendering the device useless as a pressure transducer. This problem was addressed and solved in the prior art by employing either alpha-silicon carbide or beta silicon carbide as both a sensor network and as the diaphragm. For example, see U.S. Pat. No. 5,165,283 entitled HIGH TEMPERATURE TRANSDUCERS AND METHOD OF FABRICATING THE SAME EMPLOYING SILICON CARBIDE issued to Anthony. D. Kurtz et al. and assigned to Kulite Semiconductor Products, Inc. the assignee herein. A heteroepitaxial growth process is described in this patent for growing alpha or beta silicon carbide on silicon substrates to fabricate pressure transducers capable of operating at extremely high temperatures in excess of 600° C.
The alpha silicon carbide (6H SiC) and beta silicon carbide is (3C SiC) described in U.S. Pat. No. 5,165,283, are just two of 200 different polytypes identified in SiC. Beta silicon carbide, however, has some distinct advantages over alpha silicon carbide. One advantage is that there is no limit on the size of the wafers that can be used in fabricating the pressure transducers. Another advantage is that beta silicon carbide is, overall, much easier and less time consuming to fabricate than growing alpha silicon carbide. Furthermore, beta silicon carbide is much less costly to fabricate than alpha silicon carbide.
Beta silicon carbide exhibits gauge factors of above 30 at room temperature and gauge factors of between 10-15 at 550° C. Thus, beta silicon carbide's ability to operate at temperatures above 500° C., while exhibiting basically temperature independent gage factors of 10-15 at such temperatures, and providing a 10 factor improvement in sensitivity over the metal gages, makes beta silicon carbide a very plausible material for high temperature applications. Moreover, the technology for processing beta silicon carbide in terms of metallization, etching, and patterning, has been demonstrated by the prior art in patents such as U.S. Pat. No. 5,165,283.
Although prior art semiconductor devices made from beta silicon carbide films on silicon are possible, such devices made in production quantities have a high defect density. This is due to the large thermal and lattice mismatches (8% and 20% respectively) between the beta silicon carbide and the silicon which causes poor quality p-n junctions in beta silicon carbine. Hence, attempts at providing semiconductor pressure transducers microfabricated from beta silicon carbide have been generally unsuccessful.
It is, therefore, a primary object of the present invention to provide a semiconductor pressure transducer device made from beta silicon carbide which avoids the problems associated with the prior art devices.
SUMMARY OF THE INVENTION
A high temperature pressure transducer comprising a diaphragm fabricated from beta-silicon carbide and at least one sensing element fabricated from beta-silicon carbide associated with the diaphragm. The sensing element associated with the diaphragm such that it is dielectrically isolated therefrom by an oxide layer.
The high temperature pressure transducer described above is made in accordance with a method that comprises the steps of depositing a diaphragm layer of beta-silicon carbide on a surface of a first semiconductive wafer, forming a dielectric isolation layer on the layer of beta-silicon, fabricating at least one sensing element made from beta-silicon carbide on a second semiconductive wafer, bonding the second wafer to the first wafer so that the sensing element is disposed on the dielectric isolation layer, and micromachining an aperture in the first semiconductive wafer to enable a portion of the diaphragm layer of beta-silicon transversing the aperture to deflect when a force is exerted thereon.
REFERENCES:
patent: 5303594 (1994-04-01), Kurtz et al.
Kurtz Anthony D.
Ned Alexander A.
Kulite Semiconductor Products
Morris Duane
Oen William
Plevy Arthur L.
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