Patent Publication Number: US-2009225556-A1

Title: Thermoelectric cooler and illumination device using same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to the following commonly-assigned copending applications: Ser. No. 12206171, entitled “ILLUMINATION DEVICE” (attorney docket number US 18668). Disclosures of the above-identified application is incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present invention generally relates to component cooling, and particularly to a thermoelectric cooler having high heat transfer efficiency, and an illumination device using the thermoelectric cooler. 
     2. Description of Related Art 
     In recent years, due to excellent light quality and high luminous efficiency, light emitting diodes (LED) have increasingly been used to substitute for cold cathode fluorescent lamps (CCFL) as a light source of an illumination device, referring to “Solid-State Lighting: Toward Superior Illumination” by Michael S. Shur, or others. on proceedings of the IEEE, Vol. 93, NO. 10 (October, 2005). 
     LEDs generate a significant amount of heat when working, with stability thereof affected by temperature. When the temperature of the LED is too high, light intensity of the LED may be attenuated gradually, shortening life of the device. Thus, a thermoelectric cooler may be used to transfer heat from the LED to a heat dissipation device, from which the heat can be dissipated efficiently. The thermoelectric cooler typically includes a cold end and a hot end, both of insulated material with high thermal resistance, such as ceramic, the thermoelectric cooler operating correspondingly on the Peltier effect. Thermal conductive adhesives are widely used to adhere the thermoelectric cooler to a printed circuit board (on which the LEDs are mounted), with the heat dissipation device acting as bonding medium. Heat dissipation efficiency of the illumination device is limited due to the high thermal resistance of the thermal conductive adhesive. 
     What is needed, therefore, is a thermoelectric cooler with improved heat transfer efficiency used in an illumination device which can overcome the described limitations. 
     SUMMARY 
     A thermoelectric cooler includes a plurality of P-type semiconductor elements, a plurality of N-type semiconductor elements, a plurality of connection circuits, a cold end and a hot end. The P-type semiconductor elements are electrically connected to the N-type semiconductor elements by the connection circuits. The P-type semiconductor elements, the N-type semiconductor elements and the connection circuits are sandwiched between the cold end and the hot end providing thermal connection therebetween. The cold end includes a first metal base and a first insulated metal oxide film formed on a side of the first metal base adjacent to the P-type semiconductor elements, the N-type semiconductor elements and the connection circuits. 
     Other advantages and novel features of the present thermoelectric cooler will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present thermoelectric cooler and illumination device can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present thermoelectric cooler and illumination device. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a cross-section of a thermoelectric cooler, in accordance with a first embodiment of the present invention. 
         FIG. 2  is a cross-section of a second insulated metal oxide film of the cold end of  FIG. 2 . 
         FIG. 3  is a cross-section of an illumination device, in accordance with a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Referring to  FIG. 1 , a thermoelectric cooler  10 , in accordance with a first embodiment, comprises a plurality of P-type semiconductor elements  11 , a plurality of N-type semiconductor elements  13 , a plurality of connection circuits  15 , a cold end  12  and a hot end  14 . 
     The connection circuits  15  are connected in series. The P-type semiconductor elements  11  are connected to the N-type semiconductor elements  13  by the connection circuits  15 . The cold end  12  is arranged opposite to the hot end  14 . The P-type semiconductor elements  11 , the N-type semiconductor elements  13  and the connection circuits  15  are sandwiched between the cold end  12  and the hot end  14 . 
     The P-type and N-type semiconductor elements  11 ,  13  can be tellurium compounds, such as bismuth telluride or antimony compounds. The connection circuits  15  can be metal such as aluminum, tin, silver, copper, gold and alloy, or others. 
     The cold end  12  of the thermoelectric cooler  10  comprises a metal core printed circuit board (MCPCB)  120  and a first insulated metal oxide film  122 . The metal core printed circuit board  120  includes a first metal base  1200 , a copper foil layer  1202 , and an insulated layer  1404  sandwiched between the first metal base  1200  and the copper foil layer  1202 . The hot end  14  of the thermoelectric cooler  10  comprises a second metal base  140  and a second insulated metal oxide film  142 . 
     The first and second insulated metal oxide films  122 ,  142  correspond to the first and second metal bases  1200 ,  140 , respectively. The first insulated metal oxide film  122  is formed on the first metal base  1200  by application of a layer of anodic aluminum oxide (AAO). For example, when forming the first insulated metal oxide film  122 , the metal core printed circuit board  120  with the first metal base  1200  thereof connected to an anode can be immersed in electrolyte containing acidizing fluid, such as sulfuric acid, oxalic acid, phosphoric acid or chromic acid fluid. The anode is electrically connected to a power source. The first metal base  1200  and the acidizing fluid react to form the first insulated metal oxide films  122 . In the embodiment, the first metal base  1200  is preferably metal with high thermal conductivity, such as aluminum, and an aluminum oxide film  1220  is formed thereon. As shown in  FIG. 2 , the aluminum oxide film  1220  has a plurality of void structures  1221  defined away from the first metal base  1200 . The void structures  1221  are uniformly arranged and filled with insulated materials  1224 , such as monox, alumina, spin on glass (SOG), organic compounds, or others. It can be understood that the second metal base  140  may also be aluminum, and the second insulated metal oxide films  142  may be formed on the second metal base  140  by application of a layer of anodic aluminum oxide. Therefore, the second insulated metal oxide film  142  and the first insulated metal oxide film  122  have the same structure. 
     The first and second insulated metal oxide films  122 ,  142  can be formed by other methods, such as macro-arc oxidation (MAO). During formation of the first insulated metal oxide films  122  on the first metal base  1200  by MAO, the metal core printed circuit board  120  with the first metal base  1200  thereof connected to an anode is immersed in electrolyte containing halides solution, such as potassium hydroxide or silicate. The anode is electrically connected to a power source, and the micro-arc discharges electricity from a surface of the first metal base  1200 . Thus, the surface of the first metal base  1200  is melted, and the first insulated metal oxide films  122  is sintered on the first metal base  1200 . In this embodiment, the first metal base  1200  is an aluminum layer with a depth of 0.5 mm, and depth of the first insulated metal oxide films  122  formed on the first metal base  1200  is approximately 0.2 mm. 
     The first and second metal bases  1200 ,  140  are metal with high thermal conductivity, and the first and second insulated metal oxide films  122 ,  142  are metal oxide films corresponding to the first and second metal bases  1200 ,  140 . Thus, the first and second insulated metal oxide films  122 ,  142  also have high thermal conductivity, increasing heat transfer efficiency from the cold end  12  of the thermoelectric cooler  10  to the hot end  14 . 
       FIG. 3  shows an illumination device  50 , in accordance with a second embodiment. The illumination device  50  comprises at least one solid-state light source  56 , a heat dissipation device  58 , and the thermoelectric cooler  10  of the first embodiment. The thermoelectric cooler  10  is employed in the illumination device  50 , transferring heat generated by the at least one solid-state light source  56  to the heat dissipation device  58 , where the heat is dissipated to the atmosphere. 
     The at least one solid-state light source  56  includes a plurality of LEDs. The LEDs can be white or multicolored such as red, green and blue. The LEDs  56  are mounted on the copper foil layer  1202  (a circuit is defined on the copper foil layer  1202 ) of the metal core printed circuit board  120  by eutectic bonding or solder bonding. 
     The heat dissipation device  58  comprises a base  582  and a number of fins  580  extending from the base  582  and substantially perpendicular to the base  582 . The base  582  is coupled on the second metal base  140  of the hot end  14  by eutectic bonding or solder bonding, and thermally contacts the hot end  14 . 
     During operation, an exterior power supply  59  having an anode and a cathode is applied to supply power to the thermoelectric cooler  10 , wherein the P-type and N-type semiconductor elements  11 ,  13  are electrically connected to the anode and the cathode, respectively. Heat is generated from the LEDs  56  during illumination. When the power supply  59  supplies electric current to the thermoelectric cooler  10 , electrons with negative electricity in the N-type semiconductor elements  13  move to the anode, and holes with positive electricity in the P-type semiconductor elements  11  move to the cathode. Heat generated by the LEDs  56  is thus transferred to the hot end  14  from the cold end  12  of the thermoelectric cooler  10  by electrical energy. The heat accumulated on the hot end  14  of the thermoelectric cooler  10  is immediately dissipated via the fins  580  of the heat dissipation device  58 , from which the heat is dissipated to the atmosphere. Thus, by the provision of the thermoelectric cooler  10 , efficiency of the heat dissipation of the LEDs  56  is improved, such that illumination device  50  operates continually within an acceptable temperature range, achieving stable optical performance. 
     It is believed that the present invention and its advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.