Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – In combination with or also constituting light responsive...
Reexamination Certificate
2002-08-14
2004-01-27
Fahmy, Wael (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
In combination with or also constituting light responsive...
C257S099000, C257S100000, C257S098000
Reexamination Certificate
active
06683325
ABSTRACT:
Reference to related U.S. patents and application, the disclosures of which are hereby incorporated by reference:
U.S. Pat. No. 5,391,523, Marlor;
U.S. Pat. No. 5,606,218, Cotter et al.;
Published PCT application PCT/DE96/01728 (U.S. designated)
Reference to related patents and publications:
European published application A 603 933, published Jun. 29, 1994, Filmer;
German published application DE 195 47 567 A1, Varga et al.;
“White-light diodes are set to tumble in price”, by Philip Hill, OLE, pp. 17 to 20, October 1997;
Proceedings of the Second International Conference on Nitride Semiconductors
, ICNS'97, articles by D. Steigerwald: “Reliability Behavior of GaN-based Light Emitting Diodes”, p. 514-515; and
“High Power UV InGaN/AlGaN Double Heterostructure LEDs”, by Mukai, Morita and Nakamura, p. 516.
FIELD OF THE INVENTION
The present invention relates to opto-electronic semiconductor elements, particularly suitable for general illumination, and especially adapted to be used with luminescence or light wavelengths conversion phosphors, in which the respective components of the semiconductor element, when integrated to form a light source, are so constructed that thermal coefficients of expansion of the respective elements are similar, and to a method of manufacturing such elements. The light emitting elements are, for example, light emitting diodes (LEDs), which emit light in the region of between about 320 to 1600 nm. Preferably, the LEDs emit ultraviolet (UV) light, and are used in combination with luminescence conversion materials to emit white or other visible light. These elements can then be used for general illumination purposes. It is also possible to use the elements to emit UV radiation, without luminescence conversion. The semiconductors usually utilize a nitride of gallium, and/or indium and/or aluminum.
BACKGROUND OF THE INVENTION
Opto-electronic semiconductors, for example LEDs, are restricted in their possibility of application. Up to now, these restrictions have not been considered serious. Plastics are thought as ideal housings for the semiconductors, since they can be easily worked, or cast. Resin casting technology, using epoxides, is widely employed. The apparently ideal suitability plastics as a material for the housings cover a defect, however, namely the mismatch of the expansion behavior of the respective elements, upon changes in temperature. Using the customary plastic housing limits the temperatures arising in manufacture and/or operation to the region of from −55° C. to +110° C. When used with very short wavelengths, in the UV range, the housing degrades rapidly.
Light-emitting diodes, providing white light, have recently been considered for general illumination purposes. The LED itself emits blue, or UV light, from which white light is generated. General illumination structures are customarily based on radial arrangements, suitable for insertion mounting. Luminescent conversion by LEDs, also known as LUCOLED designs, are typical. Surface mount structures are also used, particularly for TOPLED designs for surface mount LEDs. The article “White-light diodes are set to tumble in price” by Philip Hill, OLE, October 1997, pp. 17 to 20, describes details of such structures. The LUCOLED design, for example, utilizes blue emitters based on GaN, from which, by luminescence conversion, white light is generated.
The article “High Power UV InGaN/AlGaN Double Heterostructure LEDs” by Mukai, Morita and Nakamura, describes the construction of a UV-emitting LED with an emitting wavelength of about 370 nm. The LED has a chip secured to a circuit support frame, and cast in a plastic housing.
LEDs of different colors are investigated and described in the article “Reliability Behavior of GaN-based Light Emitting Diodes” by D. Steigerwald. This article, as the one referred to above by Mukai et al., is published in the “Proceedings of the Second International Conference on Nitride Semiconductors”—ICNS' 97, pp. 514-515 and p. 516, respectively. It was determined that the degradation of the LED substantially increases with shorter emission wavelength down to about 470 nm. The determinative portions of the degradation are the factors of operating current and surrounding temperature, as well as the housing of plastic material. For the investigation, the epoxy resin housing was temporarily removed.
Overall, it appears that operating a UV-emitting LED will not lead to success, since the UV radiation damages the housing. If a blue emitting LED is used as a light source, the emitted light, and efficiency is relatively low, about 5 lm/W. Earlier opto-electronic semiconductor elements had a housing formed of a metal-glass system. A glass lens was fitted into a metal cap—see, for example, published PCT publication PCT/DE96/01728. This solution met higher requirements relating to the optical characteristics; manufacturing costs, however, for a base plate and for the lens cap are very high, overall manufacture is expensive, and high tolerances during manufacture and adjustment permit only limited use of such technology. Optical perfection of the system, thus, is not suitable for many applications.
SUMMARY OF THE INVENTION
It is an object to provide an opto-electronic semiconductor element, and a method for its manufacture, which permits manufacture and/or use in a wide range regarding temperature and ambient humidity, and is suitable for operation in a wavelength region of between 300 nm to 1600 nm, and which is simple to manufacture.
Briefly, the semiconductor element has a semiconductor body which can receive, or emit, radiation. Since the semiconductor body can receive or emit radiation, the term “radiation active” will be used herein to cover both the reception, as well as emission, of radiation. This radiation active semiconductor is secured to an electrically conductive base frame, and is surrounded by a gas-tight housing. In accordance with a feature of the invention, all materials used for the housing and the base frame have temperature coefficients of expansion, within the temperature range which arises in manufacture and use, which are matched to each other.
Preferably, the housing has a base body with a recess, in which the base body is secured to the base frame in gas-tight manner. The semiconductor is a semiconductor chip, secured in the recess of the base frame, and the recess is closed off gas-tightly by a cover. In accordance with a feature of the invention, the base body and/or the cover is made of glass or quartz glass, or a ceramic, or a glass-ceramic. The respective materials are optimally matched to each other in the temperature range of from −60° C. to 150° C. This permits a junction temperature T
1
of, at this time, about 100° C. to 130° C., and even higher. Use of LEDs in an outside region up to a surrounding temperature of about 100° C. becomes possible, so that it is useful in automotive applications or in out-of-door information systems.
The semiconductor element in accordance with the present invention has the advantage that conventional methods can be used to attach the semiconductor chip on the conducive frame under high temperature conditions. The plastic housings used heretofore do not permit such attachment, due to the temperature sensitivity of the plastics. In accordance with a feature of the present invention, conductive adhesives which, for example, contain silver, are used.
The element in accordance with the present invention has another advantage, namely that the stability is enhanced, since boundary layer effects between the semiconductor chip and plastic housings are avoided. No delamination arises in long-term operation, nor during soldering. Thus, the light output coupling is stabilized.
Practice of the present invention has the particular advantage that, first and basically, the possibility is offered to provide a UV-emitting LED which has high light output and efficiency while, at the same time, the element can be inexpensively made. This is not only due to the basically simple concept of manufacture, but als
Langer Alfred
Waitl Guenter
Weitzel Reinhard
Cohen & Pontani, Lieberman & Pavane
Fahmy Wael
Ha Nathan W.
Patent-Treuhand-Gesellschaft-für Elektrische Glühlampen mbH
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