Electric lamp and discharge devices – Cathode ray tube – Screen
Reexamination Certificate
2000-05-26
2001-12-11
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Screen
C313S470000, C359S265000, C359S266000, C359S267000
Reexamination Certificate
active
06329748
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to flat panel display devices and more particularly, to a membrane-free phase transition flat panel display utilizing Vanadium Dioxide (VO
2
)-based pixels, employing a thick aerogel film as a heat resistant material, to electrically modulate light utilizing the phase transition property of VO
2
.
BACKGROUND OF THE INVENTION
Application of Vadium Dioxide (VO2) based pixels for electrically modulating light utilizing the phase transition property of VO2 is well known in the art. VO2 exhibits an insulator-to-metal phase transition at a temperature T
c
=68° C. which is accompanied by a significant change in electrical and optical properties. Due to this feature, this material has been utilized in various electrical and optical applications. These applications have included: a medium for holographic optical recording, a temperature stabilizer and controller, an electronic switch, material for screening and modulating microwave radiation and electronic and optical memory elements. One of the optical properties which is significantly changed during the phase transition is the index of refraction, which enables VO
2
to modulate light reflectance. The phase tansition in VO
2
can be thermally induced by utilizing heater elements disposed under the film of this material. This feature can be utilized in the flat panel displays. An example of such a phase transition flat panel display is described in co-pending patent application Ser. No. 08/791,032 entitled “Phase Transition Flat Panel Display”, incorporated herein by reference.
The prior art phase transition flat panel display comprises a plurality of individual VO2 based pixels, arranged in a conventional two dimensional matrix array fabricated on silicon substrates. Each pixel includes an optical resonator comprising a film of VO2 disposed on top of an aluminum mirror element A film of polysilicon is disposed beneath the mirror element and acts as a heater element to heat the VO2 film to cause the phase transition of the pixel. An air gap is provided between the polysilicon heater film and the silicon substrate layer to minimize heat dissipation through the substrate.
Each pixel interconnected by column and a row line. A diode is coupled to each pixel and implemented as a pn junction fabricated on the silicon substrate. These diodes are utilized to prevent current spread and possible cross talk between the pixel elements.
While the prior art phase transition display has been proposed to provide high speed or video frequency operation, high resolution, gray levels, and color display, its manufacturing is rather complex. First, to make the temperature decay time as long as possible and thus minimize the display power consumption, each pixel is fabricated as a membrane disposed over the air gap in the Si substrate. Moreover, to further increase the decay time, the display must operate in a vacuum. Both these factors complicate the device manufacturing and increase production cost. Second, the pixel heaters are planned to be fabricated from poly-silicon. This requires display heating for poly-Si anneal and implantation to temperatures as high as 900° C and thus makes it incompatible with the driving circuitry, which is designed to be fabricated on the same Si wafer prior to the pixel processing. Accordingly, an improved pixel structure for a phase transition display device which overcomes these problems is greatly desired.
SUMMARY OF THE INVENTION
The phase transition display device of the present invention contemplates a membrane-free pixel design utilizing a solid layer of aerogel as a heat resistant material disposed between a silicon (Si) substrate and the pixel structure, thereby eliminating the need for air gaps to thermally insulate each pixel. The phase transition display of the present invention also employs a thin film of TaSi
2
(tantalum silicide) material to act as the heater element in place of the polySi film used in the prior art. The TaSi
2
heater element is thinner than the polySi and therefore requires less heating than the polySi film. More importantly, it needs lower fabrication temperatures which makes it compatible with the processing of the drivers. A top surface of the silicon substrate is formed as small mesa “islands” surrounded by aerogel to minimize the heat transfer and thus increase the temperature decay time. A 100 &mgr;m-wide aluminum row metal lines are formed on the Si substrate beneath the pixels to maintain a high optical fill-factor while minimizing the voltage drop across row wires. The heater element is then connected to the Si-based mesas via a thin film, preferably of platinum (Pt) to further reduce any lateral heat transfer from the pixel to the silicon wafer.
REFERENCES:
patent: 3258628 (1966-06-01), Acton
patent: 4015166 (1977-03-01), Ohshima et al.
patent: 4670690 (1987-06-01), Ketchpel
patent: 5079473 (1992-01-01), Waymouth
patent: 5608568 (1997-03-01), Blodgett et al.
Chudnovskiy Feliks
Halioua Maurice
Kastalsky Alexander
Naar Sylvain
Shokhor Sergey
Copytele Inc.
Duane Morris LLP
Patel Ashok
Plevy Arthur L.
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