On-chip integrated silicon carbide pressure and temperature sensors

An integration of silicon carbide (SiC) pressure sensor and a temperature sensor on a single SiC substrate to facilitate the simultaneous measurement of pressure and temperature at temperature, and a method of fabricating the same.

FIELD

The present invention generally pertains to sensors, and more particularly, to on-chip integrated silicon carbide (SiC) pressure and temperature sensors to facilitate the simultaneous measurement of pressure and temperature at temperature.

BACKGROUND

Pressure sensing in aero-engine combustion chambers is becoming of increased importance for the experimental validation of computational fluid dynamics (CFD) codes used in engine model predictions. Currently, there is high uncertainties in CFD codes, more pronounced in the high temperature regime of model prediction.

Experimental validation of CFD codes is necessary in order to improve their accuracy, thereby reducing the existing high level of uncertainties. It is also desirable to monitor in real-time low magnitude pressure transients that manifest the onset of thermoacoustic instabilities and mitigate their growth in order to prevent damage to critical engine components. The above stated needs are currently addressed with state of the art pressure transducers that are traditionally placed several feet away from the combustion chamber to prevent sensor damage while pressure is transmitted through semi-infinite tubes to the transducers.

However, the tube length and distortions in its geometry could result in acoustic reflections and/or attenuation that could lead to the loss of key frequency components or distortion.

SiC pressure sensors have been developed and demonstrated to operate at 800° C., allowing the sensor to be inserted in close proximity to the combustion chamber. However, the output response of piezoresistive based pressure sensors is sensitive to changes in temperature during pressure measurement. It, therefore, requires temperature compensation techniques that would subtract the temperature sensing component and preserve the measured pressure. Of equal importance as the pressure sensor is the temperature sensor. Pressure and temperature measurements are critical for the validation of the CFD codes and for the monitoring of engine health during flight.

The traditional approach to sensing these two events is to insert each transducer into separate borescopes in the test article, and effort would be made to locate them in close proximity as practically possible. It is known that best pressure temperature correlation is obtained when the two transducers are located as closely together as possible. In doing so, the effect of temperature on the pressure sensor would be effectively and accurately quantified so that the temperature compensation strategy that is implemented would be trusted. The state of the art approach of having separate pressure and temperature transducers does not provide for such accurate translation of the temperature effect on the pressure sensor. This is because the two sensors are not located on the same chip and taps must be inserted further into the test article where temperature is as high as 800° C. Attempts to insert taps into such high temperature environment results in the destruction of the pressure sensor. There is a general reluctance on the part of engine manufacturers to have too many pressure and temperature taps than is necessary in the engine. That is why the use of a common tap for both pressure and temperature measurement is preferred. Real-time translation of pressure as function of temperature is needed in order to provide instantaneous pressure signals as the test progresses. Significant cost reduction in production and assembly is achieved, and eases path toward IC integration. Buying the pressure and temperature sensors separately is more expensive than the integration of both on a single chip.

Accordingly, an improved pressure and temperature sensor system may be beneficial.

SUMMARY

Certain embodiments of the present invention may be implemented and provide solutions to the problems and needs in the art that have not yet been fully solved by conventional pressure and temperature sensor technologies. For example, some embodiments of the present invention pertain to the integration of SiC pressure sensor and temperature sensor on a single SiC substrate to facilitate the simultaneous measurement of pressure and temperature at temperature.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Some embodiments of the present invention pertain to the integration of SiC pressure sensor and temperature sensor on a single SiC substrate to facilitate the simultaneous measurement of pressure and temperature at temperature.

FIG.1is a flow diagram illustrating a method for fabricating an integrated pressure sensor and temperature sensor on a single SiC substrate (or embedded resistor thermal detector (RTD)), according to an embodiment of the present invention. In some embodiments, method100begins with obtaining 2-μm n-type 4H-SiC epilayer102on semi-insulating 4H-SiC substrate104at105. At110, aluminum (Al)106is deposited on the 4H-SiC epilayer102, and standard photolithography is used to etch trench patterns108in the Al.

At115, method100uses the Al mask106to perform reactive ion etching into the epilayer102and semi-insulating substrate104to realize the trench112, which in the present embodiment has a serpentine structure. At120, the Al106is stripped and another Al layer114is deposited. For this, a standard photolithography is used to define and etch resistor patterns in the epilayer. Note, there is no further etching in the RTD trench112and the Al is stripped.

At125, RTD metallization stack116comprising of TaSi2(1 micron)/Pt (5 microns)/TaSi2(1 micron) is deposited into the serpentine trench and on the surface of the wafer. In this step, the RTD metallization stack116is patterned and etched in the RTD trench112. An alternative to this step is to deposit the metallization stack116into the serpentine trench through a shadow mask. At130, oxide118is deposited onto the RTD metallization stack116and is annealed at 800° C. in argon.

At135, on the backside122of the RTD metallization stack, a nickel (Ni) seed layer is deposited and then the nickel (Ni) is electroplated to about 10 microns to form a nickel mask124. At140, using the nickel (Ni) mask124, use reactive ion etching to etch into the backside122to form a diaphragm with a required diaphragm thickness126. Residual Ni mask124is striped and the wafer is cleaned.

At145, using standard lithography and reactive ion etching, ohmic contacts128are created in the oxide. The wafer is then cleaned in acetone. At150, ohmic contact metallization of Ti (100 nm)/TaSi2(300 nm)/Ti (100 nm)/Pt (300 nm) is deposited and self-aligned rapid thermal anneal is performed at 800° C. Another layer132of Ti (100 nm)/Pt (300 nm) is deposited and annealed at 800° C. At155, using standard lithography and reactive ion etching, ohmic contact patterns134are created and wafer is cleaned in solvents. At160, a second oxide136is deposited, diffusion barrier vias are opened, diffusion barrier metallization of Ti (100 nm)/Pt (300 nm) is deposited, blanket rapid thermal annealed at 800° C., followed by another layer138of Ti (20 nm)/TaSi2(20 nm)/Pt (100 nm)/Au (1 micron) and anneal at 800° C. The diffusion barrier metallization is then patterned and etched by reactive ion etching, followed by deposition of a third oxide layer142.

At165, using standard lithography and reactive ion etching, bond pad vias144are created in the oxide and the wafer is cleaned in acetone. At170, bond pad metallization146is deposited and a rapid thermal anneal is performed at 800° C., and at175, standard photolithography and etching is applied to the pattern, and the RTD and pressure sensor bond pads148are etched.

FIG.2is a flow diagram illustrating a method for fabricating an integrated pressure sensor and temperature sensor on a single SiC substrate (surface resistor thermal detector), according to an embodiment of the present invention. In some embodiments, method200begins with obtaining 2-μm n-type 4H-SiC epilayer202on semi-insulating 4H-SiC substrate204at205. At215, standard lithography and reactive ion etching is used to create piezoresistive patterns and structures206in the epilayer202.

At215, silicon dioxide208is grown or deposited on the patterned piezoresistors. At220, on the backside, Ti90:Ni10 seed layer is deposited and then nickel (Ni)212is electroplated to about 10 microns.

At225, using nickel (Ni) as a mask212, reactive ion etching is used to etch onto the backside214of the wafer to a desired diaphragm thickness. In this step, residual nickel (Ni) is stripped and the wafer is cleaned. At230, using standard lithography and reactive ion etching, ohmic contact vias216are created in the oxide208to SiC surface and the wafer is cleaned in piranha clean (p-clean), which is equal volume of hydrogen peroxide and sulfuric acid.

At235, ohmic contact metallization218(as described in150) is deposited and self-aligned thermal anneal is performed at 800° C. At240, using standard lithography and reactive ion etching, ohmic contact patterns222are created and the wafer is cleansed in an acetone and isopropanol solvents.

At245, deposit a second oxide224, open diffusion barrier vias, deposit diffusion barrier metallization226(as described in160), blanket rapid thermal anneal diffusion barrier metallization, pattern and etch diffusion barrier metallization, and deposit third oxide layer. At250, RTD metallization stack228is deposited. At255, the RTD metallization stack228is patterned and etched. At260, a spin-on-glass (SOG)232is applied over wafer and cured.

At265, standard photolithography and etching is applied to open bond pad vias234in SOG and oxide-3 layers. At270, a bond pad metallization236is deposited on the wafer, and at275, apply standard photolithography and etching to pattern and etch the RTD and pressure sensor bond pads238. Finally, gold (Au)242is deposited followed by pattern and etching.

FIG.3illustrates a graph300showing temperature sensor response after two thermal excursions, according to an embodiment of the present invention.

In the example shown in graph300, the RTD was placed in an atmospheric oven and heated to 800° C. Also placed in the oven was a k-type calibrated thermocouple for reference. Temperature was then gradually raised at increments and held for 10 minutes. This was repeated at each increment up to 800° C. The process was repeated during the cooling down cycle.

FIG.4illustrates a graph400showing simultaneous measurement of temperature and zero pressure output voltage of an integrated device at different temperatures, according to an embodiment of the present invention. In this embodiment, graph400shows how the temperature affects the zero pressure output voltage and how the co-located temperature sensors provides accurate measurement of the temperature. By quantifying the relationship between the temperature and the zero pressure output, an effective temperature compensation scheme can be implemented.

FIG.5is a diagram illustrating a cross sectional view of a backend packaging500for an integrated pressure sensor and temperature sensor on a single SiC substrate, according to an embodiment of the present invention. In some embodiments, backend packaging500includes a dam505composed of nickel (Ni), which is welded to an alloy tube510to prevent leaks. The alloy tube510may be any suitable alloy such as an iron-Nickel-Cobalt alloy. Commercially available alloy tubes include tubes sold under the trademark KOVAR. A nickel (Ni) tube515is closed at the top to also prevent leaks. Ni tube515may extend into aluminum nitride (MN) shoulder520.

Non-porous dielectric material (or fill)540is hermetically attached to nickel (Ni) tubes515and nickel (Ni) dam505. It should be noted that any metal material may be used to prevent leaks between nickel (Ni) tubes515and non-porous dielectric material540. A pair of gold (Au) wires535extending across the length of nickel (Ni) tubes515extend into AIN header525. Wires535may breach through AIN header525and extend into sensor530.

In some embodiments, dam505and alloy tube510are seal welded. These seal welds prevent leakage from any joints starting from the tip of the sensor.

The package may be composed of four structural components. For example, the structural components may include a sensor bearing surface mounted header, surface mounted header adapter, alloy tube, and a stainless-steel dam.FIG.6Ais a diagram illustrating a sensor bearing surface mounted header600A, according to an embodiment of the present invention. Header600A may receive an integrated pressure and temperature sensors chip. There are seven through holes601-607that receive wires that connect to the integrated pressure and temperature sensors chip. Two of the seven holes are dedicated for the RTD while the remaining five holes are for the pressure sensor. The wires (not shown) make contact with the contact pads of the chip and then extend through the holes to the external back end of the package.

FIG.6Bis a diagram illustrating a surface mounted header adapter600B, according to an embodiment of the present invention. In some embodiments, the narrow neck of header600A ofFIG.6Aslides into the receptacle608of adapter600B. A high temperature glass paste may be applied to the narrow neck of header600A before it is slid into adapter600B. The glass paste is then cured at 800° C. in atmosphere for 15 minutes. This process results in the sealing of the joint between header600A and adapter600N, thereby preventing leaks.

The wires (not shown) that are connected to the chip on header600A, which pass through the seven holes that are also in adapter600B. These holes in adapter600B may align with the seven holes in header600A.

FIG.6Cis a diagram illustrating an alloy tube600C, according to an embodiment of the present invention. The smaller outer dimension neck of adapter600B slides into alloy tube600C and is then brazed with a high temperature braze alloy at 800° C. for up to 15 minutes. The brazed joint between the ceramic AlN adapter and the metallic alloy tube is brazed to ensure that no leak occurs.

FIG.6Dis a diagram illustrating a stainless steel dam600D, according to an embodiment of the present invention. In some embodiments, dam600D receives the other end of alloy tube600C. Alloy tube600C is partially inserted into the hole made through the dam. The outer diameter surface of Alloy tube600C makes contact with dam600D. In some embodiments dam600D is subsequently seal welded to prevent leaks.

FIG.6Eis a diagram illustrating a final package assembly600E, according to an embodiment of the present invention. In this embodiment, the wires (not shown) that are in contact with the chip extend through the above components shown in final package assembly600E. In order to prevent the wires from breakage, they are individually inserted through small tubes of nickel. Each nickel tube is slid into each hole of header600A, through adapter600B, through alloy tube600C, through dam600D, and to the outside. To prevent the nickel tube (with wire inside) from touching each other and causing electrical shorts (nickel being an electrical conductor), each individually inserted into small ceramic tubes. These ceramic tubes, just like the nickel tube, extend from the holes inside header600A, through the holes inside adapter600B, through alloy tube600C, and terminate halfway inside dam600D. Dam600D is filled with a ceramic paste and cured at high temperature to create a non-porous solid filling, thereby rigidly holding the spread out nickel tubes (wire inside each), rigidly holding the small ceramic tube sheaths (wire and nickel inside each), and rigidly attached to the inner wall of dam600D. The only parts sticking out of dam600D are the nickel tubes, each with a corresponding wire to facilitate external electrical connection. This allows the measurement of pressure and temperature to be performed.