Radiant energy – Radiant energy generation and sources – Plural radiation sources
Reissue Patent
1999-01-29
2001-04-24
Anderson, Bruce C. (Department: 2881)
Radiant energy
Radiant energy generation and sources
Plural radiation sources
C250S50400H
Reissue Patent
active
RE037146
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to image projection and particularly, infrared (IR) image projection from an array of tightly packed resistively heated microstructure emitters that requires relatively small amounts of electrical power to drive the emitters. The microstructure array operates at cryogenic temperatures in order to simulate low-radiance space backgrounds and at room temperatures for earth-bound backgrounds.
BACKGROUND OF THE INVENTION
A major challenge in IR projector array technology is to produce a high-emittance structure that requires relatively little electrical power during operation. Resistor arrays are one popular approach to obtaining IR scene projectors capable of wide dynamic range.
Typically, an array designed for projecting radiation in the IR spectrum will have a large number of discrete pixel structures coupled to drive electronics. Arrays can be fabricated with a wide range of pixel sizes and pitches to meet the requirements of a specific optical systems. A representative array of the prior art may have 96 pixels and operates in the short-wavelength IR (SWIR) to the long-wavelength IR (LWIR) wavebands. The arrays may be optimized to a desired wavelength of projection purpose, such as generating dynamic radiation clutter scenes or multiple independently moving targets against a background that simulates conditions in the upper atmosphere of Earth. Variations in the thermal and electrical properties of the array are achievable via modification of the pixel, considering collimator optics and field of view (FOV) requirements of the desired application.
A critical parameter of thermal radiating projection elements is known as the thermal time constant “T”, defined by “T”=C/G, where G is the thermal conductance between the heated element and a substrate associated with the element, and C is the thermal mass of the heated element. To achieve high-speed performance necessary to display dynamic IR scenes a pixel must have a short thermal time constant. Thus, a successful design will exhibit a thermal time constant that is a fraction of the frame rate at which the projector operates. Given as thermal time constant of millisecond duration, the pixels must be heated to many hundreds of degrees above ambient temperature to display high radiance scenes using only milliwatts of power per pixel. However, thermal isolation between adjacent pixels and the substrate associated with the pixel must be maintained to limit cross talk among adjacent pixels in the array.
The array electronics are relied upon to control pixel temperatures and maintain temperatures between frame updates for reduced image flicker. Traditionally located beside the IR arrays, recent advanced in CMOS addressing electronics and fabrication techniques have lead to a two-level IR array structure with the electronics disposed beneath a pixel emitter associated therewith, so that high fill factors may be achieved with pixels covering virtually the entire surface of the IR array.
SUMMARY OF THE INVENTION
The high performance, low power IR scene projector array of the present invention benefits from high radiance efficiency due to the low power requirements, high fill factors, and high emittance of the resistively heated microstructure emitters. Furthermore, the present invention exhibits response over a large dynamic range due to the low substrate temperature and the high temperature materials used in the fabrication of the instant invention.
The array operates in a two-level architecture wherein the array resides suspended on support legs, which provide a very low thermal leakage path, and the array electronics are disposed underneath the array in a compact and efficient manner so that high fill factors result.
A vacuum environment and use of low thermal conductance materials serve to isolate the entire assembly from thermal transients. High optical emissivity results from the tuned optical cavity design and deliberate selection of emitter and special films chosen to optimize optical properties of the array.
Low temperature operation properties of the instant invention result from careful selection of the resistor, pixel films, and the electronics.
The emitter resistor has a large operating temperature range via: low negative thermal coefficient of resistance (TCR) in the 20-650 degree Kelvin temperature range is ideally suited to a drive mode of projection driven by electrical current, the pixel resistance of about 40 kOhms provides optimal heating at low electrical current levels, and the emitter material has a resistance of about 1 kOhm per square, thereby permitting use of a 40 square serpentine pattern which fits into the small pixel geometry. The emitter thermal design accounts for low temperatures: silicon nitride films, implementations of a cold heat sink that reduces effective hot conductance by 50%, and pixel design pre-adjusted for temperature-dependent time constants.
The pixel has millisecond response time and no “flicker” because: thermal conductance defines radiance decay, heating power controls radiance increase, flexible design covers a wide range of time constants, and the non-refreshed current droop measures less than one percent after five minutes. The pixel field effect transistor (FET) benefits from excellent low temperature characteristics through the use of radiation hardened (radhard) RICMOS electronics, FET conductance improved by a factor of two at 20 degrees Kelvin, and carrier freeze out does not affect performance. The pixel time constant is adjustable by changing the length of the support legs that couple the array to the substrate.
To achieve very high speed performance, collimating microlens assemblies couple to each emitter pixel allows the emitter to be smaller and thus have a shorter time constant for the same thermal conductance while simulating a 100% fill factor. The microlens also allows the
size
use of reduced-size emitters and thus the thermal response time of the pixel is decreased thereby leading to increased frame rates.
Two level architecture, bearing hybridized pixel drive electronic beneath the supported emitters capable of operating at near-room temperature significantly improves on the prior art and represents the latest iteration of this advance IR scene projection technology.
REFERENCES:
patent: 2983283 (1961-05-01), Oberly
patent: 4510558 (1985-04-01), van den Brink
patent: 4530010 (1985-07-01), Billingsley
patent: 4639603 (1987-01-01), Pistor
patent: 4654622 (1987-03-01), Foss et al.
patent: 4724356 (1988-02-01), Daehler
patent: 4859080 (1989-08-01), Titus et al.
patent: 4922116 (1990-05-01), Grinberg et al.
patent: 5021663 (1991-06-01), Hornbeck
patent: 5077563 (1991-12-01), Takeuchi et al.
patent: 5159480 (1992-10-01), Gordon et al.
patent: 5214292 (1993-05-01), Hendrick, Jr.
patent: 5245369 (1993-09-01), Um et al.
patent: 5300788 (1994-04-01), Fan et al.
patent: 5610637 (1997-03-01), Sekiya et al.
patent: 5657060 (1997-08-01), Sekiya et al.
patent: 2274943 (1994-08-01), None
patent: 9326050 (1993-12-01), None
D.R.Stauffer et al, article “Thermal Scene Pprojectors Using Microemitters”, Bellingham US Nov. 1991 vol. 30, No. 11, pp. 1664-1667.
G.H.Chapman et al, article “A Wafer Scale Dynamic Thermal Scene Generator”, International Conference on Wafer Scale Integration, Jan. 22-24, 1992, San Francisco, CA.
M. Parameswaran et al, article “Commercial CMOS Fabricated Integrated Dynamic Thermal Scene Simulator”, International Electron Devices Meeting, Dec. 8-11, 1991, Washington, pp. 753-756.
R.G.Driggers et al., article “Review of Infrared Scene Projector Technology—1993”, from Optical engineering, vol. 33, No. 7, Jul. 1994, Bellingham, pp. 2408-2416.
M.Parameswaran et al., article “Micromachined Thermal Radiation Emitter From a Commercial CMOS Process” from IEEE Electron Device Letters, Feb. 12, 1991, vol. 12, No. 2, pp. 57-59.
B.E.Cole et al, article “512×512 Infrared Cryogenic Scene Projector Arrays”, Honeywell Technology Center, Feb. 7, 1995, pp. 193-202.
B.W. Ludington, “Ultra-Low-Power Scene Projector for Targets
Cole Barrett E.
Han Chien J.
Anderson Bruce C.
Honeywell International , Inc.
Shudy, Jr. John G.
LandOfFree
Low power infrared scene projector array and method of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Low power infrared scene projector array and method of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Low power infrared scene projector array and method of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2469253