THIS INVENTION concerns peltier devices and methods of constructing and operating same.

Peltier devices are intended to transfer heat energy by absorption and dissipation, and can be operated efficiently only if it is possible to ensure sufficient heat absorption at one side of the device, complete transfer of the absorbed heat across the device, and efficient heat dissipation from the other side.

Conventionally, such devices comprise a metallic heat absorption sink, a metallic heat dissipation sink and semiconductor pillars electrically driven and disposed between the two sinks but electrically insulated therefrom usually by end plates of a ceramic material which, though electrically insulating must be of a thickness in the order of 0.5mm for mechanical strength and are thus poor thermal conductors.

In patent publication GB 2247348, improved peltier devices avoid the use of thick ceramic end plates and are characterised by a microns-thin layer of an electrically insulating material bonded to opposed surface regions of the two heat sinks, an electrically conductive layer superimposed on each coating of electrically insulating material, and a layer of semiconductor material disposed between the two electrically conductive layers, the

component parts of the entire device being bonded together as a consolidated structure.

An object of the present invention is to provide a further improved form of peltier device.

According to the present invention, there is provided, a peltier device comprising a heat absorption sink and a heat dissipation sink disposed in face-to-face relationship with a semiconductor material interposed between them, electrical supply means for the semiconductor material, and a microns-thick layer of an electrically insulating material disposed between the semiconductor material and each heat sink; characterised in that the semiconductor material and the layers of electrically insulating material are interposed between a pair of end plates at least one of which is of such dimensions as to extend beyond an area thereof occupied by the semiconductor material and includes means to enable direct attachment of said at least one end plate to another surface.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:-

Fig. 1 is an end view of a conventional peltier device;

Fig. 2 is an isometric view of a peltier device made in accordance with one embodiment of the present invention;

Fig. 3 is a view similar to Fig. 2 of a peltier device to be disposed between secondary heat sinks in a practical application;

Fig. 4 is an end view of a further embodiment of a peltier device made in accordance with the invention;

and Figs. 4a to 4g are schematic illustrations of various alternative forms of a part of a peltier device made in accordance with the invention.

A conventionally constructed peltier device is illustrated in Fig. 1. Two ceramic end plates 10 and 11 each of the same size and shape and mounted symmetrically i.e. identically aligned with respect to each other. The end plates 10 and 11 are some 0.5mm in thickness and are thus very poor thermal conductors.

Since the two end plates 10 and 11 are separated by an assembly of semiconductor pillars 12 which are in the order of 1mm across, the two end plates 10 and 11 have only a space of 1mm between them, and the semiconductor pillars 12 occupy substantially the entire internal space between the two plates. Accordingly, there is very little available space either between the two end plates 10 and 1 1 or across the intervening space between them which could provide room for access to means for mounting primary, secondary or further heat sinks with respect to the end plates.

For example, it would not be practicable to mount screw

heads, to accommodate fixing holes, or to provide space for and access to nuts or other fixing means in order to attach the peltier device to the adjacent heat sinks 13 and 14. Furthermore, the end plates 10 and 1 1 , being typically of a ceramic material, although quite thick have inadequate mechanical strength for the peltier device to be bonded directly or indirectly to the associated heat sinks.

Referring now to Fig. 2, there is illustrated an improved arrangement of peltier end plate in which the plates 10a and 11a are not symmetrical i.e. in this example each plate is of elongated rectangular form and the two plates are mounted with their major axes arranged in different directions and preferably at right angles to each other. As shown in Fig. 2 the end plate 10a may have holes to receive fixing bolts, and the end plate 11a may have threaded studs. Alternatively, only one plate may have fixing means, or both plates may have the same fixing means, all whereby one or both plates can be easily attached to a heat sink of the appliance with which the peltier must operate e.g. the cabinet structure of a refrigerator or freezer.

The material of the end plates 10a and 11a may be more thermally conductive than those of the conventional peltier device illustrated in Fig. 1 , and the end plates themselves may form the primary means of heat absorption and heat dissipation but are readily attached if necessary to secondary heat absorption and heat dissipation sinks of the appliance. This is illustrated in Fig. 3 where a secondary metallic heat absorption sink 13a is provided with threaded studs 'A' which are received by the holes 'B' in the end

plate 10a, and a secondary metallic heat dissipation sink 14a includes holes 'd' which receive the threaded studs 'c' of end plate 11a.

Referring now to Fig. 4, there is illustrated a means of construction whereby secondary metallic heat absorption and heat dissipation sinks 15 and 16 respectively may be made self-supporting and may clamp the peltier device between them without any risk of damaging the more delicate end plates 10a and 11a of the device. In this example, the heat dissipation sink 16 is configured to provide a supporting platform 17 which engages the outer surface of end plate 11 a, the end plate 10a being fixed against the surface of the heat absorption sink 15. Threaded studs 18 extend outwardly from the heat absorption sink 15 and carry resilient supporting bushes 19, and the heat dissipation sink 16 has apertures whereby it may be located on the threaded studs 18 and clamped thereto by nuts 20. The platform 17 of the heat dissipation sink 16 has apertures greater than the diameter of studs 'c' on end plate 11a and is secured by further nuts 21 applied thereto. During assembly, the heat dissipation sink 16 is advanced towards the heat absorption sink 15 so that the two parts meet and engage accurately on the threaded studs 18, before the platform 17 engages the studs 'c\

It will be appreciated that the means of attachment of the end plates 10a and 11a to their respective secondary heat sinks may be by any suitable fastening devices and the outer ends of the end plates may be configured accordingly and may be of a shape other than rectangular.

The end plates 10a and 11a may be of a good thermally conductive material such as aluminium with a microns-thick coating (typically l Oμm - 150μm) of ceramic based dielectric or other electrically insulating material deposited onto the adjacent surfaces of the two plates. This may be achieved by a high-temperature bonding and curing process or alternatively by a cold contact bond.

A typical power supply to peltier devices of this kind may be in the form of a an electrically conductive track printed onto the electrically insulating material and delivering 12 volts at 70 watts. In the operation of the device this causes one of the end plates to become hot and the other to become cold. The heat is absorbed from and by the secondary heat sinks, and the device relies for efficient operation upon the heat being taken away from the hot end plate at least at the same rate as it is being presented to it. If the heat is not removed at the required rate then the device operates against a "thermal back pressure". This means that the energy being fed into the device is not being effectively used because the heat is not being dissipated at a sufficient rate. This energy must be dissipated in some manner and would be given off as heat thus exacerbating the problem of heat dissipation.

If, accordingly, the energy input is reduced according to the rate of dissipation, it is conceived that the system would be more efficient in operation. Thus, temperature sensors may be incorporated into the device thus to determine the temperature of one or both end plates either directly from the end plates themselves of from the

associated heat sinks to which they are attached.

To achieve this as illustrated in Fig. 4a of the accompanying drawings on each of the end plates, (end plate 10a is shown) preferably outside of the area 22 in which the semiconductor pillars are placed, there may be provided one or more further coatings 23 of a dielectric substance onto which a sensing track is deposited such that conductivity of the track would change with temperature and this conductivity can be measured so that the surface temperature may be known.

Accordingly, the actual temperature of the two end plates can be measured and monitored very accurately and with immediate effect since the response time of such sensing elements is very short. Such a temperature sensing device is of considerable advantage when compared with, for example, thermocouples which are not so accurate and are relatively slow to respond as well as often displaying characteristics of hysteresis.

Thus there is provided a peltier device which incorporates a built-in temperature sensing means within the body of the device itself.

As illustrated in Figs. 4b to 4f, the temperature sensing coatings/tracks 23 may be disposed in many different positions in relation to the position of the semiconductor pillars, and as illustrated in 4g, may be placed on the external surface of the end plate.