Measuring and testing – Fluid pressure gauge – Diaphragm
Patent
1993-02-26
1994-06-21
Woodiel, Donald O.
Measuring and testing
Fluid pressure gauge
Diaphragm
29 2542, G01L 912
Patent
active
053219899
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The present invention relates to an integratable capacitative pressure sensor, particularly of the type which includes a semiconductor substrate and a polycrystalline semiconductor film, which define a pressure sensor cavity and which is provided with a dopant at least within a diaphragm-like area located above the pressure sensor cavity; a process for manufacturing such an integratable capacitative pressure sensor; and an integratable capacitative pressure sensor array.
A pressure sensor of the type in question as well as a process for its manufacture are already known from the following technical publications: for Pressure Transducer Arrays", IEDM 1984, pages 223 to 225. Transducers 185, Philadelphia 1985, pages 90 to 92.
Such a prior art pressure sensor is shown in FIG. 6. In the process for manufacturing this known pressure sensor, a silicon substrate 1 has first applied thereto a spacer film 2, which is also referred to as spacer. This spacer film 2 defines a future pressure sensor cavity 3. The spacer film 2 has deposited thereon a polysilicon film 4.
FIG. 7 shows a top view of the pressure sensor according to FIG. 6. As is clearly evident especially from FIG. 7, the spacer film 2 is provided with extensions extending through the polysilicon film 4 and defining etching passages 5 which permit the guard film 2 to be removed from below the polysilicon film 4 by means of etching. When the spacer film 2 has been etched away, the etching passages 5 will be closed. Depending on the process executed, a vacuum or a gas pressure, which can be adjusted to a defined value, will remain in the pressure sensor cavity 3. The polysilicon film 4 has a diaphragm-like structure, which is adapted to be deformed by external pressure. The degree of deformation can be converted into an electrical signal by applied piezo-resistive resistors.
The deformation of the diaphragm, which consists of the polysilicon film 4, can also be detected capacitively, as is, for example, explained in the following technical publication: Sensor Technology", Y. Phys. E. Sci. Inst. 20 (1987), pages 1469 to 1471.
For capacitively detecting the deformation of the diaphragm-like polysilicon film 4, the polysilicon film 4 can be doped heavily by implantation in the area of a diaphragm region 6, whereby a counterelectrode to the electrode formed by the substrate 1 is produced, as will especially be evident from FIG. 8.
Such a known pressure sensor is, however, not compatible with CMOS (complementary metal oxide semiconductor) circuits. Furthermore, the capacitance of the known pressure sensor depends on the voltage applied, since a non-ohmic resistance is created between the polysilicon film 4 and the silicon substrate 1. Furthermore, due to the resistance formed by the non-implanted region of the polysilicon film 4, the charge of the known pressure sensor has to be detected with a specific frequency. Hence, the known pressure sensor is not suitable for detecting pressure changes by means of low-frequency sampling read-out circuits. Nor can the known pressure sensor be used for monolithic integration with additional electronic circuit elements.
German Patent DE 37 23 561 Al discloses a capacitative pressure sensor structure having a multi-layer, comparatively complicated structure. A lower insulating layer is formed on a substrate, the lower insulating layer having provided thereon a diaphragm support layer, which encloses a pressure sensor cavity. The diaphragm support layer is coated with a cover layer for closing the pressure sensor cavity. Only the diaphragm support layer, but not the cover layer, consists of a polycrystalline semiconductor material. A semiconductor zone, whose dimensions correspond essentially to those of the pressure sensor cavity located above the semiconductor zone, is defined within the substrate by a doping opposite to the doping of the substrate.
In the case of such a pressure sensor, the total capacitance of the sensor element is determined, on the one hand, by a pressure-dependent capacitance in the area of
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Eichholz Jorg
Kandler Michael
Manoli Yiannakis
Mokwa Wilfried
Zimmer Gunther
Dougherty Ralph H.
Fraunhofer-Gesellschaft zur Forderung der Angewandten Forschung
Oen William L.
Woodiel Donald O.
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