BACKGROUND ART A large number of transistors are integrated in the main chip comprising the CPU of computer. According to"Moor's Law", that is, the price of the chip goes down by a half while the performance of the chip increases by twofold, the degree of integration is expected to increase further. For example, there are 42,000, 000 transistors in the Intel pentium4 chip, which is prevailing nowadays. According to"Moor's Law", it is prospected that 250,000, 000 transistors can be integrated into CPU until the year of 2010. As the degree of integration increases, as predicted by"Moor's Law", more energy is used in the calculation process of chips and more heat is generated on the surface of the chips. The performance of the semiconductor is sensitive to the temperature. As a result, the problem of the treatment of the large amount of heat generating on the surface of the chip, is in great concern.

In prior art, a cooling fan was attached to the surface of CPU, and additional fin was added to enhance the cooling effect. But, the cooling fan makes much noise and does not adequate for the notebook computer or mobile communication device, which are in the trend of miniaturization.

To solve above-mentioned problems, the micro cooler is being vigorously i

researched, which is the size of semiconductor chip and can be attached to the chip directly, for the maintenance of constant temperature of the chip. The mainstream of this research is the passive type micro-cooler, which does not require additional power source. There are many passive type micro-cooler: the micro-cooler, where the material with high conductivity is place between the heat producing chip (high temperature part) and the low temperature part so that the heat is transferred from the high temperature part to the low temperature part; the micro-cooler, where the heat generated at the high temperature part evaporates the refrigerant and the evaporated refrigerant give off the heat to the low temperature part by convection. The latter kind of micro-coolers comprises CPL (Micro Capillary Pumped Loop), Micro Heat Pipe or the combination of Micro Heat Pipe with heat spreader et al. But, above-mentioned passive type micro- cooler has too small capacity to meet the great amount of heat produced at the currently used semiconductor chip.

To meet the above-mentioned shortages, an active type micro-cooler with the structure of ordinary cooler was developed, which is composed of compressor, evaporator, expansion valve and condenser, and operated by an additional external power source to maximize the cooling capacity. In the development of above- mentioned active type micro-cooler, the need for the development of micro-compressor is emphasized. But, the micro-compressor is hard to be manufactured at the size of semiconductor chip, and the capacity is relatively small.

DISCLOSURE OF THE INVENTION The present invention was devised to solve above said problems of the prior art, and the purpose of present invention is to provide a micro-cooler which is small but has

enough cooling capacity to be applied to the semiconductor chip.

The purpose of present invention is achieved by providing micro-cooler, comprising a evaporator which is directly attached to the heat source and vaporizes refrigerant; a compressor which inhales and compresses the vaporized refrigerant gas; a condenser which condenses the compressed refrigerant gas and discharges heat from the refrigerant ; a conduit which directs condensed refrigerant to the evaporator; and a expansion valve which is mounted on conduit and expands the condensed refrigerant.

It is preferred that, the evaporator is equipped with a heat transfer channel on a sheet member which has a surrounding wall around it; and a certain number of connecting channels which enable the vaporized refrigerant gas to move to said compressor.

It is preferred that, the compressor is equipped with a certain number of compression means which are arranged symmetrically on a sheet member, compress the refrigerant beneath said sheet member and then send the compressed refrigerant to the upper side of said sheet member; and a center hole which enables the condensed refrigerant from the condenser to move toward said evaporator.

It is preferred that, the vibrating plate is operated by symmetrically arranged a certain number of piezo-actuators, and the inlet valve and the outlet valve operated by piezo-actuators which are disposed on said inlet valve and said outlet valve respectively It is preferred that, the condenser is equipped with a certain number of connecting channels which enable the vaporized refrigerant gas to move to the compressor, a heat transfer channel on a sheet member which has a surrounding wall around it, and a center hole, which enables the condensed refrigerant from the condenser to move toward said evaporator.

It is preferred that, the conduit is connected to the center holes that are formed on said compressor and condenser.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects of the present invention will become more readily appreciated and understood from a consideration of the following detailed description of the preferred embodiment when taken together with the accompanying drawings, where: Fig. la is a perspective view of the notebook computer equipped with active micro-cooler, according to the present invention; Fig. lb is a perspective view of the active micro-cooler according to the present invention; Fig. lc is a broken perspective view of the active micro-cooler according to the present invention; Fig. 2a, 2b, 2c, 2d, and 2f are a perspective view of evaporator of the micro- compressor according to the embodiment of the present invention; Fig. 3 is a cross-sectional perspective view of the insulating plate of the active micro-cooler according to the present invention; Fig. 4 is a perspective view of the compressor of the active micro-cooler according to the present invention; Fig. 5a is a plane perspective view of the compression means comprising the compressor of the active micro-cooler according to the first embodiment of the present invention;

Fig. 5b is a rear perspective view of the compression means comprising the compressor of the active micro-cooler according to the first embodiment of the present invention; Fig. 5c is a cross-sectional perspective view of the compression means comprising the compressor of the active micro-cooler according to the first embodiment of the present invention; Fig. 6a, 6b and 6c are the views that illustrate the operation principles of the piezo-actuator which is used as a driving means for the compression means of the micro-cooler according to the present invention.

Fig. 7a, 7b, 7c, 7d, 7e, 7f and 7g are the views of the compression means of the micro-compressor according to the present invention, illustrating the operating procedures of the compression means.

Fig. 8a is a plane perspective view of the compression means comprising the compressor of the active micro-cooler according to the second embodiment of the present invention; Fig. 8b is a rear perspective view of the compression means comprising the compressor of the active micro-cooler according to the second embodiment of the present invention; Fig. 8c is a cross-sectional perspective view of the compression means comprising the compressor of the active micro-cooler according to the second embodiment of the present invention; Fig. 9 is a perspective view of the condenser of the active micro-cooler according to the present invention;

Fig. 10 is a P-h diagram, which illustrates the operation of the micro-cooler according to the present invention.

REFERENCE NUMERALS IN DRAWINGS 1 notebook computer 10 active micro-cooler 20 heat pipe 30 MPU chip 40 heat diffuser 100 evaporator 101 heat transfer channel 102 connecting channel 105 fin 200 insulating plate 201 connecting channel 202 center hole 300 compressor 302 center hole 303 connecting channel 304 penetrating hole 310 compression means 311 outlet valve 312 inlet valve 313 upper vibrating plate 314 lower vibrating plate 315 round plate 316 outlet hole 317-326 piezo-actuator 327 pressure chamber 328 inlet hole 331,332 piezoelectric element 340 compression means 341-344 flip valve 345 inlet hole 346 outlet hole 400 condenser 402 channel 403 center hole

BEST MODE FOR CARRYING OUT THE INVENTION The preferred embodiment is illustrated in the following detailed description referring to the accompanying drawings.

In Fig. la, lb and lc, an active micro-cooler according to the present invention is illustrated. As illustrated in Fig. la, the micro-cooler 10 according to the present invention can be used directly attached to the MPU 30 of computer. Fig. lb is the enlarged view of the part A, which is marked with broken line in Fig. 1 a. As illustrated in Fig. la and lb, the above micro-cooler 10 can be attached directly to MPU 30 to extract heat therefrom, which is then discharged through heat pipe 20 and heat diffuser 40. In addition to the heat diffuser 40, a fan (not illustrated in the figures) can be attached to the upper part of micro-cooler 10.

Fig. I c is a broken perspective view of the active micro-cooler according to the present invention. As illustrated in Fig. lc, the micro-cooler 10 according to the present invention comprises: a evaporator 100 which is directly attached to the heat source and vaporizes refrigerant; a compressor 300 which inhales and compresses the vaporized refrigerant gas; a condenser 400 which condenses the compressed refrigerant gas and discharges heat from the refrigerant; a conduit which directs condensed refrigerant to the evaporator; and a expansion valve which is mounted on conduit and expands the condensed refrigerant.

As illustrated in Fig. la, lb and lc, in the active micro-cooler 10 according to the present invention, the evaporator 100 is directly attached to the object to be cooled (MPU 30, in this embodiment. ) And the evaporator 100, the compressor 300, and the condenser 400 are layered in sequence, to form laminated structure. As a result, the present invention can be compactly assembled in a multi-layered structure.

But, the present invention is not limited to the laminated structure. The evaporator 100, the compressor 300, and the condenser 400 can be arranged in a same plane, or only a few of them can be put into multi-layered structure according to the circumstances. Also, the evaporator 100, the compressor 300, and a condenser 400 can be placed with a certain distance to prevent the counter-flow of heat.

Fig. 2a, 2b, 2c, 2d, and 2f are a perspective view of evaporator of the micro- cooler according to the embodiment of the present invention. As illustrated in Fig. 2a, 2b, 2c, 2d, and 2f, the evaporator 100 includes sheet member which has a surrounding wall around it; and a certain number of connecting channel 102 which enable the vaporized refrigerant gas to move to said compressor 300. Preferably, the shape of the sheet member of the evaporator 100 is round, and additional heat transfer channel can be installed to increase the evaporation capacity. The centrifugal channel 101 is recommended for the heat transfer channel, so that the refrigerant, supplied from above, can advance from the center area to the periphery. The shape of the cross-section of the centrifugal channel 101 can assume the shape of rectangle (Fig. 2b), triangle (Fig. 2c), convex (Fig. 2d) or concave (Fig. 2e). Also, plurality of fin 105 can be used as a heat transfer channel. The plurality of fin 105 can assume the shape of cylinder or square pillar. The evaporator 100 is directly attached to the MPU 30, and vaporizes refrigerant with the heat generating at the MPU 30.

The evaporator 100 can be mass-produced through micro-molding using the mold which is processed with LIGA process, semiconductor process or micro electric discharge machining process.

Fig. 3 is a cross-sectional perspective view of the insulating plate 200 of the active micro-cooler according to the present invention, which is located between the

evaporator 100 and the compressor 300, or compressor 300 and a condenser 400. It is recommended that the insulating plate 200 is installed between the evaporator 100 and the compressor 300, or compressor 300 and a condenser 400, to prevent the counter- flow of heat from the high temperature part to the low temperature part.

The insulating plate 200 can be mass-produced through micro-molding using the mold which is processed with LIGA process, semiconductor process or micro electric discharge machining process.

Fig. 4 is a perspective view of the compressor of the active micro-cooler according to the present invention. As illustrated in Fig. 4, the compression means 300 is provided with a certain number of penetrating holes 304, where the compression means 300 is accommodated. The penetrating holes 304 are symmetrically arranged on the sheet member, and the accommodated compression means 310 compresses the refrigerant beneath the sheet member and then send it to the upper side of the sheet member. A center hole 302 is formed at the center of the compressor, and the center hole 302 is used as a conduit, through which the condensed refrigerant from the condenser 400 flows toward evaporation 100. It is preferred that diameter of the center hole 302, formed on the round plate, is about several tens of, m.

In the present embodiment, as illustrated in Fig. 4, six compression means 310 are symmetrically arranged in the penetrating hole along the circumference of the round sheet at the angle of 60°. The diameter of the round sheet can be made around 1 Omm and the diameter of the compression means can be made around 2mm Fig. 5a, 5b and 5c are the perspective views of the compression means comprising the compressor of the active micro-cooler according to the first embodiment of the present invention. As illustrated in Fig. 5a, 5b and 5c, compression

means equipped to the compressor of the active micro-cooler according to the first embodiment of the present invention, the compression means 310 comprises: the lower vibrating plate 314 and the upper vibrating plate 313, which are attached to the upper and lower side of the round plate 315 respectively; outlet hole 316, which is formed on upper vibrating plate 313; and inlet hole 328, which is formed on lower vibrating plate 314. The lower vibrating plate 314 and the upper vibrating plate 313 are operated by the piezo-actuators 317,318, 319,320, 322,323, 324,325 which are symmetrically arranged on the vibrating plate 313,314, and the outlet hole 316 and the inlet hole 328 are opened or closed by the outlet valve 311 and the inlet valve 312, which are comprised of flip and the piezo-actuators 321,326 attached on the flip. In Fig. 5c, the large arrow denotes the flowing direction of the refrigerant and the small arrow denotes the opening of closing direction of the outlet valve 311 and the inlet valve 312.

The compression means 310 are produced through semiconductor procedures.

That is, the compression means 310 are divided into several adequate number of layers, and every layer is processed by wet etching, DRIE (Deep Reactive Ion Etching) or CVD (Chemical Vapor Deposition) in combination with the Photolithography, and the processed layers are joined by wafer bonding process to form a symmetrical structure.

And, also, the outlet valve 311 and the inlet valve 312 can be produced through using sacrificial layer. The compression means 310 can be produced through LIGA (Lithographie, Gavanoformung, Abformung) as well as semiconductor procedures.

Fig. 6a and 6c are the side view of the piezo-actuator used as a driving means for the micro-compressor according to the present invention.

As illustrated in Fig. 6a, the piezo-actuators, which are operating the compression means 310, are formed through inserting elastic body 333 between a pair

of sheet-shaped thin piezo-electric element 331,332 and then joining said piezo- electric element 331, 332 and elastic body 333 together. The piezo-electric element 331, 332 have the characteristics of being extended of contracted according to the direction of the electric currents. In the piezo-actuators illustrated in Fig. 3a, the piezo-electric element 331 is contracted when applied with forward voltage, and the piezo-electric element 332 is extended when applied with reverse voltage. As the piezo-electric element 331, 332 are firmly joined together, the piezo-actuator bends to the direction of contracting piezo-electric element 331.

To the contrary, in the piezo-actuators illustrated in Fig. 6a, the piezo-electric element 331 is extended when applied with reverse voltage, and the piezo-electric element 332 is contracted when applied with forward voltage. As the piezo-electric element 331,332 are firmly joined together, the piezo-actuator bends to the direction of contracting piezo-electric element 332.

Like the method illustrated above, when the piezo-electric element 331,332 of the piezo-actuators 317,318, 319,320, 321,322, 323,324, 325,326 are applied with different direction of voltage, the piezo-actuators 317,318, 319,320, 321,322, 323, 324,325, 326 deform as illustrated in Fig. 6a, 6b and 6c. Generally, the piezo-actuator has the characteristics of small time constant (i. e. quick reaction rate) and precise control, and it can generate large force in spite of the small size. A certain number of piezo-actuators operate the compression means 310 by being attached to the upper flip 311, lower flip 312, the upper vibrating plate 313, and the lower vibrating plate 314.

Fig. 7a, 7b, 7c, 7d, 7e, 7f and 7g are the perspective view of the compression means of the micro-compressor according to the present invention, illustrating the operating procedures of the compression means.

As illustrated in Fig. 7a, the outlet valve 311 and the inlet valve 312 of the compression means 310 are closed in the stationary state. As illustrated in Fig. 7b, in the opened inlet valve 312 state, the center area of the upper and lower vibrating plate 313,314 subside inwardly and at the same time the inlet valve 312 is opened slightly, reducing the volume of the pressure chamber 327 and letting small amount of refrigerant to go out through the inlet hole 328. As illustrated in Fig. 7c, in the refrigerant inhalation state, the outlet valve 311 is closed and the center area of the upper vibrating plate 313 swells outwardly and at the same time the inlet valve 312 is opened widely and the lower vibrating plate 314 swells outwardly. At this state, the pressure of the pressure chamber 327 is lowered causing the refrigerant to flow in. As illustrated in Fig. 7d, in the closed inlet valve 312 state, the inlet valve 312 is closed with the inhaled refrigerant. As illustrated in Fig. 7e, in the refrigerant compressing state, the center area of the upper and lower vibrating plate 313,314 subside inwardly and with the outlet valve 311 and the inlet valve 312 closed, thus compressing the refrigerant inside the pressure chamber 327. As illustrated in Fig. 7f, in the outlet valve 311 opened state, the outlet valve 311 is opened to discharge the compressed refrigerant, which was compressed while the center area of the upper and lower vibrating plate 313,314 subside inwardly. As illustrated in Fig. 7g, in the outlet valve 311 and the inlet valve 312 closed state, the outlet valve 311 and the inlet valve 312 of the compression means 310 are closed and return to the stationary state of Fig 7a, finishing one cycle of the operation of compression means 310.

The compressor with the first embodiment of the compression means according to the present invention has the strong points of relatively simple structure and easy control as a driving means, and the present invention can be easily made into a small

size of 10mm of compressor diameter and 2mm of compression means diameter by employing piezo-actuators 317,318, 319,320, 321,322, 323,324, 325,326.

Accordingly, the present invention can be used as a micro-machine like active micro- cooler.

Fig. 8a, 8b and 8c are illustrated the second embodiment of the compression means 340 according to the present invention.

As illustrated in Fig. 8a, 8b and 8c, the compression means 840 according to the present invention is equipped with upper and lower vibrating plate 313,314 which are disposed on the round plate 315, and a pair of flip disposed on the vibrating plate 313, 314. A pair of flips 341,342 disposed on the upper vibrating plate 313 operates as the outlet valve, and a pair of flips 343,344 disposed on the lower vibrating plate 314 operates as the inlet valve. The portion where a pair of flips 341,342 meets each other becomes the outlet hole 346, and the portion where a pair of flips 343,344 meets each other becomes the inlet hole 345.

The outlet valve and the inlet valve, which are comprised of upper and lower vibrating plate 313,314 and flips, are operated by piezo-actuators as in the first embodiment of present invention.

In Fig. 8c, the large arrow denotes the flowing direction of the refrigerant and the small arrow denotes the opening of closing direction of the flips 341,342, 343,344 of the outlet valve and the inlet valve.

The compression means 340 according to the second embodiment of the present invention has the same operation procedures with the first embodiment: all flips closed; inlet valve opened; refrigerant sucked-in; inlet valve closed; sucked-in refrigerant compressed; and outlet valve opened.

In the second embodiment of the present invention, where the compression means 340 employs a pair of flip valves, the compression ratio, which is determined by the change rate of the volume of the pressure chamber, can be increased without enlarging the entire size of the device. That is, by employing upper/lower vibrating plate 313,314 and a pair of flip valves 341,342, 343,344 rather than employing just one flip valve, the volume of the pressure chamber can be further increased.

Fig. 9 is a perspective view of the condenser 400 of the active micro-cooler according to the present invention. As illustrated in Fig. 9, the condenser 400 comprises: a certain number of connecting channels 402 which enable the vaporized refrigerant gas to move to said condenser; a heat transfer channel on a sheet member which has a surrounding wall around it; and a center hole 403, which enables the condensed refrigerant from the condenser to move toward the said evaporator 100.

The condenser 400, like the evaporator, can be placed on the empty site on the sheet plate which comprises the condenser 400, or it can be additionally equipped with heat transfer channel, as illustrated in Fig. 2b, 2c, 2d, 2e, 2f.

The condenser 400 can be mass-produced through micro-molding using the mold which is processed with LIGA process, semiconductor process or micro electric discharge machining process.

Fig. 10 is a P-h diagram, which illustrates the operation of the micro-cooler according to the present invention. As illustrated in Fig. 10, the refrigerant is vaporized by heat source at evaporator 100 (@o (2)), the evaporated refrigerant gas flows though connecting channel 304 formed at the lower part of compression means 310, by way of the connecting channel 102 of the evaporator. In here, the inhaled refrigerant vapor is compressed at the compressor 300 (()). The compressed refrigerant flows to the

condenser 400 through the connecting channel 304 of the compressor, formed at the upper part of compressor 300. The inhaled refrigerant vapor, which is introduced through the connecting channel 402 of the condenser, discharges the heat to the high temperature part of the cooler while being condensed to liquid phase (Z-4). The condensed refrigerant is introduced to the evaporator 100 through the conduit, which is formed by the mutually connected center holes 302,202 of the insulating plate 200 and compressor 300. A expansion valve is installed on the conduit, and the pressure of the condensed refrigerant is lowered by the expansion valve before the condensed refrigerant returns to the evaporator 100 (@- (D).

INDUSTRIAL APPLICABILITY As illustrated above, the present invention provides a active micro-cooler with a relatively simple structure, large compression capacity and easy operation.

The active micro-cooler according to the present invention has a simple structure and large cooling capacity in comparison with the passive micro-cooler. By employing piezo-actuator as a driving means, which is easy for control, capable of precise control and has small time constant with a quick reaction-rate, the micro-cooler can be easily made into a small size of around 10mm of diameter and around 5mm of height. And in spite of the small size, micro-cooler according to the present invention can perform a precise and swift operation.

The forgoing embodiment is merely exemplary and is not to be construed as limiting the present invention. The present teachings can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.