Technical Field

The invention relates to thermoelectric devices for cooling micro- and optoelectronics devices.

Background Art

Operation of electronic devices (e.g., transistors, integrated circuits, laser diodes, etc.) is accompanied by their heating. As temperature increases the device characteristics usually deteriorate (for example, noise level increases, gain decreases, useful power decreases, etc. depending on a device type). Further increase of temperature can lead to a failure of the device. This problem is especially important for high-speed devices used for data transmission and data processing.

To stabilize or to reduce temperature of an operating electronic device an air cooling or water cooling can be used. Their disadvantages are large size and additional consumption of electric power.

Thermoelectric devices based on the Peltier effect are generally used for cooling micro- objects (e.g., U.S. patents Jfs 3006979, 3409475, 4859250). They comprise one or several pairs of electrodes, made of materials with different Peltier coefficients. As electric current flows through such junctions, heat absorption occurs in the area of one contact (group of contacts) of dissimilar materials, and heat release occurs in the area of another contact (group of contacts) because of the Peltier effect. An embodiment of cooling device based on the Peltier effect is multistage elements (U.S. Patents JN° 5040381, 4833889, 5385022). Another embodiment described in the Russian Federation patent N° 2310950 is a thermoelectric device based on the Peltier effect wherein absorbed in a temperature control area heat is released at switching pads which are well remote from the temperature-controlled area.

A main disadvantage of the devices based on the Peltier effect is a necessity of transmission of a current flow through them, which results in additional consumption of electric power that can be comparable to or even exceed power consumption of a micro- (opto-) electronic by a cooling device.

As a prototype of the claimed unit we chose the device described in the Russian Federation patent N° 102851 based on the cooling effect discovered by the author of the present invention. The cooling effect takes place in samples made of semiconductor samarium sulfide (SmS) where electric power generation occurs as a consequence of the thermovoltaic effect under the sample heating.

The prototype model represents a layered structure consisting of a layer of semiconductor material SmS (samarium sulfide) and a layer of a solid solution Smi _-x Yy _x S (Yy denotes one of the following elements: La, Ce, Gd, Pr, Nd, Dy, Ho, Er) with contact pads placed on the outer surfaces of the layered structure and output wires contacted to the pads, wherein the wires are electrically connected to each other through electrical load resistance. When the structure is heated temperature of the contact pad which is placed on the SmS layer grows faster than the temperature of the contact pad which is placed on the Sm _1-x Yy _x S layer, so that the contact pad on the Sm _1-x Yy _x S layer can be used for thermoregulation of the object. Excess heat released at electric load resistance can be placed at a required distance from the thermoregulation area by means of wires of necessary lengths. The prototype unit enables to realize stable and continuous cooling process of a micro-object without any source of electric power for operation of the cooling unit.

One disadvantage of the prototype is a low value of dissipated thermal power which is limited by the maximum values of current and voltage (their multiplication) that SmS/Smi _-x Yy _x S structure can generate under heating. Consequently, the prototype unit is capable of cooling the objects with weight of few grams by 30-40°C only.

Another disadvantage of the prototype is difficulty of providing a good thermal contact between the unit and the surface of the cooled electronic device. This relates to the fact that the contact surface of the cooled electronic device (e.g., the surface of the microchip substrate) is usually not ideally flat and it complicates a perfect thermal contact between the prototype unit and the cooling surface.

The proposed invention solves the problem of creating a unit that operates without an external electric power supply and can provide efficient cooling for micro- and optoelectronic devices.

A device for cooling objects of micro- and optoelectronic devices is designed in the form of multilayered coating deposited on a cooling surface. Such a multilayered coating consists of a lower metallic layer which is coated at least with one layer of Sm _\ . _x Ln _y S semiconductor material, where x=0 ÷ 0,17, y = 0 ÷ 0,15, therewith x+y <0,17, and an upper metallic layer connected with the lower metallic layer via a remote load resistance, wherein a value of at least one of "x" and "y" concentrations monotonically increases along the direction from the lower metallic layer towards the upper metallic layer. Therein Ln represents trivalent atoms in monosulfides relating to the group III of the 6th period of the periodic table, except of Sm (Samarium). They include, for instance, atoms of Gd gadolinium and Ce cerium.

A cooling device may comprise two or more layers of Smi _+x Ln _y S semiconductor material successively deposited in such a manner that a value of at least one of the concentrations "x", "y" increases from one layer to another one along the direction from the lower metallic layer towards the upper metallic layer, whereas both concentrations "x" and "y" are approximately constant within each of the said layers.

An operation principle of the device is based on the fact that when a multilayered coating is deposited onto the surface of a micro- optoelectronic object a reliable thermal contact is achieved even if a surface to be cooled is not planar. The first deposited metallic layer and all subsequent layers of the multilayered structure replicate the initial surface roughness thus providing perfect thermal contact of the multilayered structure to the surface.

The operation principle of the device is also based upon the fact that in a semiconductor structure with a gradient concentration of excessive atoms of samarium Sm (gradient of "x" concentration) and/or a gradient concentration of doping atoms Ln of the lanthanide family (gradient of "y" concentration) takes place generation of electric voltage (thermal e.m.f.) by means of the thermovoltaic effect induced by the heat, which is released by the object to be cooled down.

The device operates as follows. A thermal contact occurs between the lower metallic layer and the surface to be cooled down. While an object to be cooled (an opto- or microelectronic device) operates, a release of the heat takes place. Current starts to flow owing to generation of thermal e.m.f. in electric circuit that is formed by the lower and the upper metallic layers of the multilayered structure, where the layers are connected via remote load resistance. In turn, the current flow leads to heating of the load resistance and to heat dissipation in a region which is spatially separated from the cooled object.

Thus, the proposed device transforms released heat from a surface to be cooled down into electric power, which then again transforms into heat dissipated at a remote load resistance. Cooling is achieved because of heat removal from an object.

The author of the present invention discovered that the thermovoltaic effect is enhanced if either in samarium sulfide SmS or in Sm, _+x S (samarium sulfide containing excessive atoms of samarium) is created a non-uniform concentration of doping atoms Ln of the lanthanide family (i.e. elements of the group III period 6 of the periodic table) manifesting a valence of 3 in compound with sulphur. The discovered phenomenon is presumably associated with the fact that an additional electron, which appears in the conduction band of samarium sulfide when a trivalent atom is incorporated into it, increases conductivity of the semiconducting compound in comparison with the initial material. As a result, there occurs an increase of a maximum value of electric power which can be generated by the device and, as a consequence, there is an increase of a maximum value of heat power which can be removed from the cooled object.

The author of the proposed invention discovered that if the concentration "x" exceeds 0.17 there takes place a release of metallic phase of samarium. In addition, the author discovered that if the concentration "y" exceeds 0.15 the thermovoltaic effect disappears because samarium ions transform into trivalent state. Moreover, if x+y exceeds 0.17 one or both of the mentioned undesirable effects take place.

The present invention is illustrated by the following drawings, where:

Fig. 1 schematically illustrates an embodiment of the claimed device comprising a single layer of Sm _1+x Ln _y S semiconductor material of gradient concentration;

Fig. 2 schematically illustrates another embodiment of the claimed device comprising two layers of Sm, _+x Ln _y S semiconductor material of different chemical compositions. The utility model may contain more than two layers of Sm _1+x Ln _y S;

Fig. 3 shows a scheme of an experimental device used to demonstrate a self-cooling effect.

The claimed device shown in Fig. 1 is deposited on a surface 1 to be cooled and comprises a lower metallic layer 2, a single layer 3 of Sm _1+!i Ln _y S semiconductor material with monotonically increasing concentration "x" 4 of excessive atoms of Sm 5 and a concentration "y" 6 of doping atoms of Ln 7, an upper metallic layer 8, an electric connection 9, remote load resistance 10.

The claimed device shown in Fig. 2 is deposited on a surface 1 to be cooled and comprises a lower metallic layer 2, two layers 3.1 and 3.2 of Sm _1+x Ln _y S semiconductor material wherein each of the layers has a concentration "x" 4 of excessive atoms of Sm 5 and a concentration "y" 6 of doping atoms Ln 7 that are nearly constant and they monotonically increase from layer to layer along direction from layer 3.1 to layer 3.2, an upper metallic layer 8, an electric connection 9, a remote load resistor 10. The invention may also contain more than two layers of Sm _1+x Ln _y S wherein each of the layers has a concentration "x" 4 of excessive atoms of Sm 5 and a concentration "y" 6 of doping atoms Ln 7 which are nearly constant and monotonically increase from a layer adjacent to the cooling surface to the most remote one.

Example 1

On a molybdenum plate 1 with the dimensions 20^20x0,75 mm, which is a surface to be cooled and at the same time is a lower contact, was made a sample (melted in a high-frequency furnace) with a layer 2 of Smj ₀₂ Gdo.o7S and a layer 3 of SmS with dimensions 8x6x4 mm (Fig.3). The resistance in such a sample was 3.2 Ohm. A metallic layer forming a contact pad 4 was deposited onto an upper surface.

In this experiment cooling was carried out by short circuit of electrodes (contact pad 4 and cooled surface 1) via a load resistance 5 which resistance was close to the resistance of the structure, R = 3 Ohm. The following equipment was used: a round-shaped drying oven 2V-151 GY 54-1-141 1-76 for sample heating; chromel-alumel thermocouples in accordance with Russian State Standard R 8.585-2001 for temperature measurements; signals were inputted to a computer via an analog-to-digital converter MD-142.

Ambient temperature was measured by the thermocouple adjoined to the layer 3. The temperature of the cooled surface was measured by the thermocouple adjoined to the cooled surface 1. When ambient temperature rose, temperature of a cooled surface increased slower than ambient temperature. When ambient temperature reached 98°C temperature of the cooled surface reached a value of 56°C and then remained stable for the whole duration of the experiment, which was about 1 hour.

Thus, by coating the layers of materials based on samarium sulfide on the cooled surface 2 the temperature of the object with 3 grams of weight was lowered by 42°C in comparison with the ambient temperature. This temperature difference was maintained without any external electric power supply. Thus was reached a self-cooling effect has been realized.

Example 2

A structure was made similar to the example 1. Then the structure was heated in vacuum for 30 minutes at T=T500°C. As a result of thermal diffusion two layers of Sm _{1 02} Gdo. ₀₇ S and SmS were fused into a single sample wherein a gradient of samarium ions (excess over the stoichiometric composition by 0 to 0.02) and a gradient of gadolinium ions (excess over the stoichiometric composition of SmS by 0 to 0.07) were formed in a ~2mm-thick interfacial region. A diffusion depth (about 1 mm) was calculated taking into account the known diffusion coefficients. Structure resistance was 1.5 Ohm.

The experimental layout and used equipment were the same as in example 1 , the exception was load resistance that was 1 Ohm. When ambient temperature rose, the cooled surface temperature increased slower than ambient temperature. When ambient temperature reached 99°C, temperature of the cooled surface reached a value of only 52°C and then remained stable for whole duration of the experiment, which was about 1 hour.

Thus, during the experiment the temperature of the object with 3 grams of weight was lowered by 47°C in comparison with the ambient temperature. The temperature difference was maintained without any external electric power supply.

The presented examples demonstrate that the coatings described in the present invention prevent overheating of a surface they are deposited onto. The coatings can be deposited on surfaces of various configurations and of different curvature.