Ultra miniature multi-hole probes having high frequency response
A pressure probe includes a longitudinal tubular housing symmetrically disposed about a central axis and having an ultra miniature conical front end and an opened back end. A plurality of aperture ports having an opening are disposed about the front end. A plurality of ultra small leadless transducers has a central active deflecting area in a semiconductor substrate, and a layer of oxide on a bottom surface. At least one sensor network is disposed within the active area on the oxide layer. A glass contact wafer is bonded to the non-deflecting portion of sensing network and has a number of apertures surrounding the active area suitable for interconnection with header. A header encloses each transducer and is of a shape and size to be positioned in an associated aperture port of the probe housing. At least one lead is coupled to a header pin extending from bottom of the aperture and directed through the bottom opening into the hollow of the probe housing.
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This invention relates to multi-hole pressure probes and more particularly to a multi-hole pressure probe containing piezoresistive sensors fabricated utilizing silicon-on-insulator (SOI) techniques.
BACKGROUND OF THE INVENTIONThe so called multi-hole pressure probe has been a standard technique for measuring mean flow angles, stagnation and static pressures for over four decades. Generally, these probes make use of the known (through experiment or analysis) geometrical variation of all static pressure on fixed shapes (sphere, cylinder, wedge, etc.) which changes in a repeatable way as a function of that shape's orientation to the flow. Since the Mach number is a unique function of the ratio of stagnation to static pressure, it can also be derived from the pressures measured by such a probe. Up to two orthogonal flow angles as well as stagnation and static pressure can be deduced from pressures measured at four or five well chosen locations on the probe (using five rather than four measurement locations generally improves the accuracy but requires a larger probe). Fewer measurements yield fewer flow variables. For example, if the probe size is a concern, then two measurements can be used to find either one flow angle or stagnation and static pressures. The static pressure ports on these steady state probes are usually connected to remote pressure transducers via long lengths of small diameter tubing. This restricts their time response to several seconds or longer.
With the advent of miniature semiconductor pressure transducers in the late 1960's the pressure transducer could be moved much closer to the measurement location by mounting it in the probe body itself, thus enhancing the time response of the measurement. Such miniature semiconductor transducers were provided by Kulite Semiconductor Products, Inc., the assignee herein. Kulite Semiconductor Products, Inc. has many patents relating to miniature pressure transducers. The development of a miniature semiconductor pressure transducer led to the evolution of a class of so called high frequency response probes, with frequency responses in the kilohertz (Khz) range. Because of the relatively high drift rate of early semiconductor transducers, these probes were only used for unsteady measurements. Conventional remote transducers, fit through separate ports for use in high accuracy measurements of the steady state values. The new technology enabled the fabrication of probes that can survive harsh environmental characteristics as determined by the needs of industry and government, aero propulsion test facilities and the like.
High frequency response of these probes are set by three factors: (1) the frequency response of the transducer (generally much higher than other factors and so not limiting); (2) the resonant frequency of any cavity between the surface of the probe and a transducer diaphragm; and (3) the vortex shedding frequency of the probe body (which scales with the probe size and the fluid velocity). The latter two factors, 2 and 3 scale with the probe size so that smaller probes will yield higher usable frequency response.
Recent advances in semiconductor transducer technology have greatly improved the stability and accuracy, as well as increase the temperature range of the transducer. These advances combine to suggest that very small probes with wider dynamic range can measure the entire frequency range from steady state to over 10 Khz. Therefore, to improve the frequency response of such probes a smaller, flatter sensor with no cavities is required. In addition, the static responses of the transducers used in the probe are limited by the static properties of the sensors used in these probes. The sensing diaphragm made by solid state diffusion uses a P-N function to isolate the sensing network from the lower underlying bulk deflecting member. Since it is made using P-N junction isolation, of course static thermal properties are now limited in their upper temperature usefulness. Recent work has resulted in the manufacture of a new type of piezoresistive sensor using SOI techniques wherein the piezoresistive network is isolated from the deflecting material by an oxide layer, while being molecularly attached to it such is shown in FIG. 1 of U.S. Pat. No. 5,286,671 entitled, “Fusion Bonding Techniques for Use in Fabricating Semiconductor Devices”, by Dr. A. D. Kurtz and assigned to Kulite Semiconductor Products, Inc., the assignee herein. The process for fabricating the composite dielectrically isolated structure requires the use of two separate wafers. The first “pattern” wafer is specifically selected to optimize the piezoresistive performance characteristics of the sensor chip, while the second “substrate wafer” is specifically selected for optimizing the micromachined capabilities of the sensing diaphragm. A layer of the higher quality thermally grown oxide is then grown on the surface of the substrate, while the piezoresistive patterns are introduced onto the pattern wafer. The piezoresistive patterns are diffused to the highest possible concentration level, equal to solid solubility, in order to achieve the most stable, long term electrical performance characteristics of the sensing network. Once the pattern and the substrate wafers are appropriately processed, the two wafers are fusion bonded together in accordance with the above-noted U.S. Pat. No. 5,286,671. The resulting molecular bond between the two wafers is as strong as the silicon itself, and since both the sensing elements and the diaphragm are made from the same material, there is no thermal mismatch between the two, thus resulting in a very stable and accurate performance characteristic with temperature. The presence of dielectric isolation enables the sensor to function at very high temperatures without any leakage effects associated with the P-N junction isolation type devices. Since the device is capable of operating at high temperatures, a high temperature metallization scheme is introduced to enable the device to interface with the header at these high temperatures.
The transducer formed by the techniques depicted in U.S. Pat. No. 5,286,671 as indicated above, enables the use of a probe which has an improved high frequency operation while being extremely small. The probe is basically a longitudinal tubular member having a front probe surface which contains holes or apertures. Each hole or aperture is associated with a separate transducer where each transducer contains a separate housing, which housing fits into the hole in the transducer probe. When mounting each transducer in its own miniature header, multiple transducers can be used simultaneously in a probe while further enabling the probe to be very small (less than 100 thousands of an inch (i.e. 100 mils) in diameter).
SUMMARY OF THE INVENTIONA miniature pressure probe, comprising: a longitudinal tubular body symmetrically disposed about a central axis and having a given diameter, the body having a front conical end and a back end, a plurality of transducer accommodating ports disposed about the front end, a plurality of leadless SOI transducers each having an active deflection area associated with a semiconductor substrate, each transducer having a header for supporting the same, with the transducer header having a thickness substantially less than the probe diameter, with each header and transducer positioned in an associated transducer port of the probe and operative to respond to flow pressure.
According to an embodiment of the invention, a multi-hole pressure probe has an internal hollow and has on the front end of the probe a plurality of apertures which communicate with the internal hollow. A pressure transducer has a first layer of semiconductor material bonded to a glass contact substrate, the semiconductor material having a central active area which deflects upon application of a force and a surface of the material is coated with an oxide layer. Positioned on the oxide layer are piezoresistive sensing elements. These sensing elements are positioned within a cavity on the glass substrate when the contact glass wafer is bonded to the semiconductor material. The glass substrate has apertures which are filled with a glass metal frit and contain header pins. The entire transducer is positioned within a separate header. A plurality of such transducers, are each positioned in its own header, and each is individually inserted into a respective aperture of the probe. This enables the measurement of flow angles, static pressures, within the structure. By mounting each sensor in its own miniature header, four or five such sensors can be used simultaneously in a probe while enabling the probe to be very small.
Referring to
Once the metallized contact barriers are defined, (using e.g. conventional photolithographic technology), the micromachining of the deflecting diaphragm takes place. The micromachining as for example, the machining of areas 40, 41 and 42 is performed using either a combination of different wet (isotropic and anisotropic) chemical processes or deep reactive ion etching (DRIE) can also be implemented. The shape and performance characteristics of the micromachined sensing or deflecting diaphragms are modeled using finite element analysis, and the SOI sensing chip is configured to be directly mounted into the probe body, thus eliminating redundancy and sensor packaging in probe installation which have historically increased the probe size. This also facilitates a better thermal match within the chip and its mount improving stability and accuracy. As indicated the piezoresistive patterns are isolated from the silicon substrate 11 by the silicon dioxide layer 12.
The layer of silicon dioxide is preferably a high quality grown oxide which is then grown on the surface of the substrate, while the piezoresistive patterns are introduced into the pattern wafer. The piezoresistive patterns are preferably diffused in highest possible concentration level equal to solid solubility, in order to achieve the most stable long term electrical performance characteristics of the sensing network. Once the pattern and the substrate wafers are appropriately processed, the two are fusion bonded together using the techniques described in the above noted U.S. Pat. No. 5,286,671 which is incorporated herein in its entirety. The resulting molecular bond between the two wafers is as strong as silicon itself and since both the sensing elements and the diaphragm are made from the same material, there is no thermal mismatch between the two, thus resulting in a very stable and accurate performance characteristic with temperature. The presence of dielectric isolation in the composite wafer 11 enables the sensor to function at very high temperatures without any leakage effects associated with the P-N junction isolation type devices.
As seen, bonded to the composite sensor 11 is a glass wafer contact wafer 16. The glass contact wafer 16 contains apertures 20. The apertures 20 eventually receive a glass metal frit to make contact to the contacts 34 associated with the piezoresistive sensors 24 and 25. The header contains a header glass layer 30 which layer is attached to the contact glass wafer by means of a glass frit bonding agent. As indicated the apertures 20 are filled with a glass metal frit and header pins 31 and 32 are inserted into each of the apertures before the glass metal frit hardens. When the glass metal frit hardens the header pins 31 and 32 are permanently retained within the glass metal frit filled apertures as 20.
Referring to
Part of the connections, as indicated in
This technology as employed in
The ceramic glass wafer which is designated as the contact glass wafer as 16 of
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Thus, in
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As seen in
The probes utilized in this type of construction are truly robust and capable of withstanding harsh environments while exhibiting excellent performance characteristics. Additionally, the new leadless assembly/packaging of the probes enables one to implement an additional center transducer as shown in
It should be obvious to one skilled in the art that there are many additional configurations that can be employed and to fabricate probes of different sizes and construction. All of these alternate embodiments are deemed to be encompassed within the spirit and scope of the claims appended hereto.
Claims
1. A pressure probe, comprising:
- a longitudinal tubular probe housing symmetrically disposed about a central axis and having an ultra miniature conical front end and an opened back end, a plurality of apertures disposed about said front end, each aperture having an opening communicating with the hollow of said housing;
- a plurality of ultra small leadless transducers, each comprised of a leadless SOI sensor and a header enclosing each transducer, the leadless sensor, being extremely thin and small is affixed onto the header, to provide a header transducer combination, said header being of a shape and size to be positioned in an associated aperture of said probe housing; and at least one lead coupled to said header pin and directed through said aperture into said hollow of said probe housing, wherein the extremely small size of the leadless transducers enables the apertures in the probe to be extremely small, spaced closely together, and appropriately angled of the air flow.
2. The pressure probe according to claim 1, wherein said semiconductor sensing element has a semiconductor substrate, said substrate having an active deflecting area on a top surface of said substrate and having a layer of oxide on a bottom surface, at least on P* doped sensor network disposed on said oxide layer and positioned within said active area, said sensor network coupled to a metal contact, a glass contact wafer bonded and having an aperture surrounding said active area, said glass wafer having a contact aperture directed from the top to the bottom of said glass wafer, said aperture contacting to said metal contact, said aperture filled with a conductive material and having a header pin extending from the bottom of said aperture to make conductive contact with said metal contact;
3. The pressure probe according to claim 2, wherein the thickness of said header transducer combination is between 10-20 mils.
4. The pressure probe according to claim 2, wherein said semiconductor substrate is fabricated from silicon and said oxide layer is a silicon dioxide (SiO2) layer.
5. The pressure probe according to claim 1, wherein said sensor is piezoresistive sensor.
6. The pressure probe according to claim 5, wherein said piezoresistive sensor is a P type silicon sensing network over silicon dioxide.
7. The pressure probe according to claim 6, wherein said glass wafer is bonded to said oxide layer by an anodic bond.
8. The pressure probe according to claim 2, wherein said conductive material is a glass metal frit.
9. The pressure probe according to claim 2, wherein said conductive material is a conductive epoxy.
10. The pressure probe according to claim 1, wherein the conical front end is truncated thereby defining a flat front surface, said flat front surface having an aperture communicating with an associated transducer.
11. The pressure probe according to claim 10, wherein said transducer measure static pressures communicating with said aperture.
12. The pressure probe according to claim 1, wherein said probe housing is cylindrical and further includes a conical front end, with said apertures are positioned on said conical front end.
13. The pressure probe according to claim 1, further including at least four transducers with each transducer having a sensor network disposed on said oxide layer and interconnected to form a Wheatstone bridge.
14. The pressure probe according to claim 1, having each transducer contain no exposed wires and have a smooth exposed surface.
15. The pressure probe according to claim 1, wherein said opening has a larger diameter top opening contiguous with a smaller diameter bottom opening, with said bottom opening communicating with the hollow of said housing and with the larger opening accommodating and enclosing said transducer header.
16. The pressure probe according to claim 14, operative to also measure stagnation pressure.
17. The pressure probe according to claim 1, wherein each transducer responds to a different flow angle pressure.
18. A miniature pressure probe, comprising:
- a longitudinal tubular body symmetrically disposed about a central axis and having a given diameter, said body having a front conical end and a back end,
- a plurality of transducer accommodating ports disposed about said front end,
- a plurality of leadless SOI transducers each having an active deflection area associated with a semiconductor substrate, each transducer having a header for supporting the same, with the transducer header having a thickness substantially less than said probe diameter, with each header and transducer positioned in an associated transducer port of said probe and operative to respond to flow pressure.
19. The probe according to claim 18, wherein said probe diameter is less than 100 mils where the thickness of said transducer header is between 10-20 mils.
20. The probe according to claim 18 further including a glass wafer bonded to said substrate and surrounding said active area to allow said area to deflect upon application of pressure thereto.
Type: Application
Filed: Dec 3, 2008
Publication Date: May 21, 2009
Applicant: Kulite Semiconductor Products, Inc. (Leonia, NJ)
Inventor: Anthony D. Kurtz (Saddle River, NJ)
Application Number: 12/315,438