Piezoelectric micro-compressor

(54) Piezoelectric micr o-compressor.

(57) The subject of the invention is a microcompressor using the piezoelectric effect.

It is constituted by a flexible membrane 1 and piezoelectric means 5 making it possible to vary the position of the membrane, this variation in position causing a variation in a predetermined volume 4, thus allowing by means of two valves 31, 32 to compress a gas .

Application to the cooling of electronic circuits.

Seekers): SPACE AND AERONAUTICAL MILITARY COMPUTING COMPANY. - FR.

(72) Inventeurfs): Christian Val.

(73) Holder):

Mandatairefs): Philippe Guilguet, Thomson-CSF, SCPI.

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FR 2 554 516

D

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PIEZOELECTRIC MICROCOMPRESSOR

The present invention relates to a microcompressor using the piezoelectric effect.

As is known, current technologies of integrated circuits and hybrid circuits and their high level of integration require the evacuation of fairly large amounts of heat, in order to guarantee thermal stability and improve the reliability of the circuits concerned.

Various solutions to this problem are currently known î

- convection cooling, using a radiator and ·, possibly a fan, which has become poorly adapted to new high-performance circuits due to its poor efficiency and its large size j

- elements, sometimes called frigistors, using the Pelletier effect; they are based on the generation of a temperature difference by two different materials subjected to a potential difference; however, they have a number of drawbacks: they have a low efficiency, require high currents which are difficult to obtain in microelectronics and, finally, they can only provide cooling at the very place where they are

2θ established;

- the expansion of a gas in a chamber located under the component or components to be cooled; this device has the drawback of requiring a high pressure gas source upstream, which is generally very bulky (compressed gas cylinder for example).

The present invention relates to a compressor capable of replacing the previous high-pressure gas source, which is miniaturized and can be manufactured using the technologies used in the field of electronic components and circuits.

More specifically, the piezoelectric microcompressor according to the invention comprises for this purpose:

- a flexible membrane fixed at its periphery on a substrate, delimiting with the latter a volume closed by at least two valves;

- Piezoelectric means animating, on electrical control, the membrane with a movement varying the closed volume.

The movement of the membrane towards the first of its two extreme positions, which increases said volume, corresponds to a so-called intake operating phase, the first of the two valves being such that it then allows the passage of a gas to an initial pressure towards the interior of the volume; the movement of the membrane towards the second of these two extreme positions which decreases said volume, corresponds to an operating phase, called compression, the second of the two valves being such that it allows the passage of gas out of the volume, at a pressure higher than the initial pressure.

Other objects, features and results of the invention res20,.

The following description will be given, given by way of nonlimiting example and illustrated by the appended drawings, which represent:

- Figure 1, a first embodiment, seen in section, of the microcompressor according to the invention;

- Figure 2, an embodiment of the electrical piezo25 means used in the microcompressor according to the invention;

- Figures 3, a, b and c, an embodiment of a detail of Figure 1;

- Figure 4, another embodiment, seen in section, of the microcompressor according to the invention;

3Q - FIGS. 5 a, b and c, different embodiments of a movement amplification device, capable of being used ·

in the microcompressor according to the invention.

In these different figures, the same references relate to the same elements and, for the sake of clarity, the actual scale of the constituent elements has not been respected.

In FIG. 1, a flexible membrane 1 has been shown, fixed on its periphery to a substrate 2 by means of a shim of thickness 61, so that the membrane 1 in the rest position (marked 11) does not touch the substrate 2 but on the contrary is provided a closed volume 4 between the membrane and the substrate. The membrane 1 is made for example of metal.

The membrane is capable of moving (arrow 12) between two extreme positions 10 and 11 under the action of piezoelectric means 5, fixed on the membrane 1 preferably near its center and supported by a cover 6, the cover being fixed also to substrate 2, for example at the periphery of the membrane.

FIG. 2 represents an embodiment of the piezoelectric means 5.

They consist of a stack of piezoelectric discs 55 between which are slid thin discs 5h of a conductive material such as copper, forming an electrode, the whole being held in position by an insulated bolt 52 and its nut 56. The discs 55 made of piezoelectric material are for example constituted by ceramics sold by the company LCC under the reference CPE 205.

The electrodes 54 are connected to an electrical supply 50, for example by means of metallized holes 64 and 65.

As is known, each of the discs is capable of elongating in the transverse direction (arrow 51) under the effect of a field applied between its two faces via the discs 54. Referring to the FIG. 1, it appears that the stack 5 described above, fixed to the membrane 1 and to the cover 6, allows the movement of the membrane as indicated by the arrow 12, thus varying the closed volume 4.

The volume 4 is capable of receiving a gas from the outside (arrow 25) via a channel 21 traced in the thickness of the substrate 2; this channel has an orifice 23 opening onto the outside of the cover 6 and, at its other end opening into the volume 4, a so-called intake valve 31 through which the gas is admitted (arrow 25) into the volume 4. Symmetrically, the substrate 2 comprises a second channel 22, closed at one of these ends by a so-called exhaust valve 32, located in the volume 4, and at its other end by a device 24 making it possible to collect the gas.

It thus appears that the device of Figure 1 operates in.

two step ;

- During the first step, the membrane 1, initially in the rest position (11) is deformed upwards towards the position 10 by the piezoelectric means 5; volume 4 is therefore enlarged and there is admission, in this volume, of gas at an initial pressure P_Q via channel 21 and valve 31;

- During the second step, the membrane 1 returns, under the action of the piezoelectric means 5, to its initial position, thereby reducing the volume 4 and compressing the gas therein; this escapes at a pressure P, greater than P_Q, through the valve

2θ 32 and channel 22 to orifice 24 where it is taken.

Figures 3a, b and c show an embodiment of the substrate 2, the channels and the valves it carries. In this figure, there is shown a partial sectional view of the substrate at the valves.

In this embodiment, the substrate 2 consists of a plurality of layers marked 26 to 29, namely, on the right part of the figure:

- A thick layer 26, forming a support, in which the intake channel 21 is engraved; this one ends with a room

34, for example circular as shown in FIG. 3c, which is a top view of the support 26 at the level of the chamber 34;

a first thin layer marked 28, covering the support 26, constituted for example by a thin sheet, comprising a hole, for example of circular section and of diameter smaller than that of the chamber 34, substantially coaxial with the latter ”

a plate 27 covering the layer 28, for example also consisting of a sheet but preferably of greater thickness, also having a hole coaxial with that of the layer 28, preferably with the same characteristics, these holes being intended to form a conduit 33 between chamber 34 and intake valve 31;

a second layer 29, covering the plate 27, preferably constituted like the layer 28, in which a cut, for example rectangular, produces the valve 31.

The device operates in the following way: during the first step described above, the piezoelectric means 5 (FIG. 1) put the membrane in its position 10, creating a vacuum above the valve 31; therefore, it is raised thereby allowing the admission of gas from the conduit 21 to the volume 4 (arrow 25).

On the left-hand side of FIG. 3a, the section of the substrate 2 at the level of the exhaust valve 32 has been shown in an analogous manner. As before, the exhaust channel 22 is hollowed out in the support 26, which is successively covered. by layer 28, plate 27 and layer 29. As previously also, the channel 22 ends in a chamber 36, for example circular and whose dimensions are preferably identical to those of the intake chamber 34; chamber 36 is shown seen from above in FIG. 3b. The valve 32 being intended to open when the diaphragm 1 passes from position 10 to position 11 (FIG. 1), so as to allow the compressed gas to pass, it is layer 28 which has a movable cutout forming the valve 32, the plate 27 being drilled as previously with a hole 35 preferably of the same dimensions as the hole 33 and the upper layer 29 is drilled with a hole preferably identical to the hole 35 in order to form a conduit 35.

The embodiment described in FIGS. 3 presents the advantage of great ease of implementation: in fact, the channels 21 and 22 are produced by milling in the support 26 and the valves are obtained by identical but symmetrical cuts, by chemical attack for example, the elements 26 to 29 being for example made of stainless steel.

FIG. 4 represents another embodiment of the microcompressor according to the invention.

In this embodiment, there is a flexible membrane i fixed on its periphery to the substrate 2 and, preferably in the vicinity of its center, to piezoelectric means 5; these are for example constituted as shown in Figure 2; the means 5 are also fixed to the cover 6, itself fixed by means of a seal 61 to the substrate 2.

In this embodiment, a bowl 203 is dug in the substrate 2 under the membrane 1, the latter carrying valves 15 and 16 closing holes 14 and 16 respectively passing through the membrane.

The device also comprises a flexible membrane 204 ensuring the seal between Ja membrane 1 and the cover 6 between the holes 14 and 16, delimiting two volumes 41 and 42.

Finally, the device has two channels, 201 and 202, allowing the volumes 41 and 42 to be connected to the outside.

The operation of this device is as follows: under the action of the piezoelectric means 5, the membrane comes to occupy a position marked 18 in the bowl 203, thus allowing the admission of gas at the initial pressure Ρθ via the channel 201 in the volume 41 and in the latter only, the valve 15 then being closed. When, still under the action of the piezoelectric means 5, the membrane 13 returns to its initial position shown in the figure, the valve 15 opens, letting the gas pass into the bowl 203. When the membrane returns to its position 18, the gas contained in the bowl 203 is compressed, therefore brought to a pressure greater than P, due to the reduction in volume of said bowl. U then escapes via the valve 7 into the volume 42 from which it can no longer exit as long as the channel 202 remains closed at its end. One thus obtains in space 42 a gas at a pressure higher than the initial pressure Ρθ.

Figures 5, a, b and c show three variants of a movement amplification device capable of being used in the microcompressor according to the invention.

In FIG. 5a, a first variant is shown in which there is a stack of piezoelectric plates as described in FIG. 2, generally marked 5, sandwiched between two flanges 57 and 58 by the bolt 52 and its nut 56. The stack is , unlike what has been described above, placed horizontally, that is to say that it provides a displacement (arrow 51) parallel to the membrane 1 and to the cover 6. The amplification device comprises four arms, marked 71 to 74, mounted so as to obtain a deformable polygon: two arms 71 and 74 connect the flanges 57 and 58 by means of three rolling needles, marked 75, placed respectively between the arms and the flanges and between the two arms; the central needle placed between the arms 71 and 74 also secures the assembly to the cover 6, for example by means of a notch (not shown) formed in the cover 6, intended to receive the needle 75. From the similarly, on the side of the membrane 1, the flanges 57 and 58 are joined by two arms (72 and 73) and three needles (75), the central needle ensuring attachment to the membrane 1 for example as on the cover 6 . In order to receive the needles 75, the flanges have shoulders and the arms are terminated at their ends by a V. Finally, the two central needles 75 are retained by a retaining spring 76.

FIG. 5b represents another alternative embodiment of the means for amplifying the movement.

In this figure, there are shown two piezoelectric stacks as described in Figure 2, marked respectively 50 and 59, placed horizontally and each connected, on the one hand, to the lateral part of the cover 6 by means of a rolling needle 63 being housed in V-shaped housings provided for this purpose in the cover and in the piezoelectric stack and, on the other hand, to a central movement amplification device, produced by a polygon constituted analogously to what is described in FIG. 5a by disregarding the piezoelectric stacks 5, that is to say by four arms such as 71 (FIG. 5a), resting on the one hand on the horizontal part of the cover 6 and on the membrane 1 and, on the other hand,, on the flanges carrying the piezoelectric stacks. Finally, one of the lateral parts of the cover 6 receiving the piezoelectric stack can be constituted by an adjustment device 62.

FIG. 5c represents a third variant of a movement amplification device.

In this figure, there is shown the substrate 2, the membrane 1 and the cover 6. As for the previous figure, this embodiment comprises two piezoelectric stacks 50 and 59 fixed on the one hand to the lateral parts of the cover 6 and d on the other hand, a central movement amplification device. It is cons2θ constituted by a liquid 79 disposed in an envelope 78, the latter being fixed on the horizontal part of the cover 6 and receiving on its lateral parts the forces exerted by the piezoelectric stacks 50 and 59. The lower part of the housing 78 is terminated by a piston 80 which moves under the action of the liquid 79 and which is in contact with the membrane 1.

By way of example, the invention has been carried out according to the mode shown in FIGS. 1, 2 and 3, with the following characteristics:

- a pressure of the order of 20 bars;

a substrate 2 consisting of a support 26 9 mm thick, two layers 28 and 29 0.1 mm thick and a plate 27 of

1mm thick, in which two conduits 33 and 35 are made, 0.6mm in diameter, these various elements being made of 23CN 18.10 steel and assembled by vacuum brazing;

- piezoelectric means comprising discs (55) 15mm in diameter, 2mm thick, having a central opening of 5mm, and electrodes 54 of the same diameters and thickness of the order of 30um, the elongation obtained for each disc under lOOOv. being of the order of 0.45um.