ELECTRON-GAS THERMOELECTRIC SENSOR

Abstract

A multilayer thermoelectric sensor for generating an electric current under the effect of heating includes a support and a thermocouple borne by the support. The thermocouple includes a first thermoelectric member having at least a portion of a bilayer, the layers of which are made of different materials, and a second thermoelectric member having a p-doped semiconductor material and/or a thermoelectric metal. The thermocouple is configured to generate an electron gas at the interface between the layers of the bilayer when the thermoelectric sensor is heated.

Claims

1. A multilayer thermoelectric sensor for generating an electrical current under an effect of heating, the thermoelectric sensor comprising: a carrier, and a thermoelectric couple borne by the carrier and comprising: a first thermoelectric member comprising at least one portion of a bilayer whose layers are of different materials, the layers of the bilayer each being undoped, and a second thermoelectric member comprising a p-doped semiconductor material and/or a thermoelectric metal, the thermoelectric couple being configured to generate an electron gas at an interface between the layers of the bilayer during the heating of the thermoelectric sensor.

2. The thermoelectric sensor as claimed in claim 1, the bilayer consisting of a layer of gallium nitride and of a layer of aluminum-gallium nitride.

3. The thermoelectric sensor as claimed in claim 1, the bilayer consisting of an upper layer and of a lower layer sandwiched between the carrier and the upper layer, the lower layer being gallium nitride and the upper layer being aluminum-gallium nitride.

4. The thermoelectric sensor as claimed in claim 3, the upper layer of the bilayer and the second thermoelectric member having first and second regions not superposed onto one another.

5. The thermoelectric sensor as claimed in claim 1, the second thermoelectric member being accommodated, at least in part, within a groove formed in the bilayer.

6. The thermoelectric sensor as claimed in claim 5, the bilayer consisting of an upper layer and of a lower layer sandwiched between the carrier and the upper layer, the groove passing through the upper layer across a thickness of the bilayer and extending into the lower layer.

7. The thermoelectric sensor as claimed in claim 6, the groove passing through the bilayer across the thickness of the bilayer.

8. The thermoelectric sensor as claimed in claim 1, the thermoelectric sensor comprising an electrically-insulating coating of an electrically-insulating material disposed between the first thermoelectric member and the second thermoelectric member.

9. The thermoelectric sensor as claimed in claim 1, the first and second thermoelectric members being in contact within an electrical connection region.

10. The thermoelectric sensor as claimed in claim 1, the thermoelectric couple comprising an electrical connector electrically connecting the first and second thermoelectric members which are at a distance from one another.

11. An electronic component comprising a thermoelectric sensor as claimed in claim 1 and an electronic unit disposed on the carrier, the electronic component being configured such that the thermoelectric sensor generates an electrical current under the effect of the heating of the electronic unit.

12. The electronic component as claimed in claim 11, the electronic unit comprising a base layer containing a material chosen from amongst gallium nitride, aluminum-gallium nitride, gallium arsenide, gallium-indium, gallium-indium nitride, aluminum nitride, and aluminum-indium nitride.

13. The electronic component as claimed in claim 11, the electronic unit comprising: a base layer comprising the material of the lower layer of the bilayer.

14. The electronic component as claimed in claim 13, the electronic unit being a power transistor in which the base layer is gallium nitride and is optionally doped.

15. A device chosen from amongst a power converter, a motor control unit, a microwave power amplifier, the device comprising an electronic component as claimed in claim 11.

16. The thermoelectric sensor as claimed in claim 4, the lower layer of the bilayer and the second thermoelectric member having first and second regions not superposed onto one another.

17. The thermoelectric sensor as claimed in claim 8, wherein the electrically-insulating coating comprises alumina.

18. The electronic component as claimed in claim 13, comprising an additional layer in contact with the base layer comprising the material of the upper layer of the bilayer, the base layer being sandwiched between the carrier and the additional layer.

19. The electronic component as claimed in claim 18, the additional layer is aluminum gallium nitride and is optionally undoped.

Description

[0171] The invention will be better understood upon reading the detailed description that follows and from the examples and by means of the appended drawings, in which:

[0172] FIG. 1 illustrates, in a transverse cross-sectional view, a step of the method of fabrication of a thermoelectric sensor according to the invention according to a first exemplary embodiment,

[0173] FIG. 2 illustrates, in a transverse cross-sectional view, another step of the method according to the first exemplary embodiment,

[0174] FIG. 3 illustrates, in a transverse cross-sectional view, another step of the method according to the first exemplary embodiment,

[0175] FIG. 4 illustrates, in a transverse cross-sectional view, another step of the method according to the first exemplary embodiment,

[0176] FIG. 5a illustrates, in a transverse cross-sectional view, another step of the method according to the first exemplary embodiment,

[0177] FIG. 5b illustrates, in a top view, the step of the method illustrated in FIG. 5a,

[0178] FIG. 6 illustrates, in a transverse cross-sectional view, another step of the method according to the first exemplary embodiment,

[0179] FIG. 7a illustrates, in a transverse cross-sectional view, another step of the method according to the first exemplary embodiment,

[0180] FIG. 7b illustrates, in a top view, the step of the method illustrated in FIG. 7a,

[0181] FIG. 8 illustrates, in a transverse cross-sectional view, another step of the method according to the first exemplary embodiment,

[0182] FIG. 9a illustrates, in a transverse cross-sectional view, another step of the method according to the first exemplary embodiment,

[0183] FIG. 9b illustrates, in a top view, the step of the method illustrated in FIG. 9a,

[0184] FIG. 10 illustrates, in a transverse cross-sectional view, another step of the method according to the first exemplary embodiment,

[0185] FIG. 11a illustrates, in a transverse cross-sectional view, another step of the method according to the first exemplary embodiment,

[0186] FIG. 11b illustrates, in a top view, the step of the method illustrated in FIG. 11a,

[0187] FIG. 12a illustrates, in a transverse cross-sectional view according to the cross-sectional plane (II), another step of the method according to the first exemplary embodiment,

[0188] FIG. 12b illustrates, in a top view, the step of the method illustrated in FIG. 12a,

[0189] FIG. 13a illustrates, in a transverse cross-sectional view, another step of the method according to the first exemplary embodiment,

[0190] FIG. 13b illustrates, in a top view, the step of the method illustrated in FIG. 13a, and

[0191] FIG. 14 illustrates, in a transverse cross-sectional view, an electronic component according to the invention fabricated according to the first exemplary embodiment,

[0192] FIG. 15 illustrates, in a top view, a step of the method according to a second exemplary embodiment,

[0193] FIG. 16 illustrates, in a transverse cross-sectional view according to the cross-sectional plane (AA), the step of the method illustrated in FIG. 15, and

[0194] FIG. 17 illustrates, in a transverse cross-sectional view according to the cross-sectional plane (CC), the step of the method illustrated in FIG. 15.

[0195] For the sake of clarity of the drawings, the proportions of the various elements constituting the electronic components illustrated are not shown to scale.

EXAMPLE 1

[0196] FIGS. 1 to 14 show a first exemplary embodiment of the method according to the invention for fabricating one example of a thermoelectric sensor according to the invention.

[0197] At the step a), as illustrated in FIG. 1, a substrate 5 is provided which comprises a carrier 10 made of silicon and a primary layer 15 of aluminum nitride which covers the substrate. For example, the thickness of the carrier e.sub.s is equal to 1.0 mm and the thickness of the primary layer e.sub.p of aluminum nitride is equal to 50 nm.

[0198] A layer 20 of gallium nitride is subsequently formed, for example by physical vapor deposition or by chemical vapor deposition, in contact with the primary layer of aluminum nitride.

[0199] A layer 25 of aluminum-gallium nitride is subsequently deposited in contact with the top face 30 of the layer of gallium nitride, as illustrated in FIG. 3, for example by physical vapor deposition or by chemical vapor deposition. The layer 25 of aluminum-gallium nitride preferably covers the top face of the layer of gallium nitride entirely. As a variant, prior to the deposition of the layer 25 of aluminum-gallium nitride, a thin electron trapping film, with a thickness for example of 0.7 nm and made of aluminum nitride, may be deposited onto the layer 20 of gallium nitride. The trapping layer is thus sandwiched between the layer 20 of gallium nitride and the layer 25 of aluminum-gallium nitride.

[0200] A bilayer 28 is thus formed, comprising a lower layer 20 of gallium nitride and an upper layer 25 of aluminum-gallium nitride.

[0201] As is illustrated in FIG. 4, at the step b), grooves are formed in the bilayer. A mask 35 is formed by photolithography on the top face 40 of the upper layer of aluminum nitride. It comprises at least one full portion 45, consisting for example of a thermosensitive resin, and recesses 50a-b being superposed onto portions 55a-b of the top face 40 of the upper layer of aluminum nitride.

[0202] The upper layer of aluminum-gallium nitride and the lower layer of gallium nitride are subsequently etched in the portions 55a-b not covered by the full portions of the mask. The etching conditions are adapted in such a manner that the portions 55a-b of the upper layer are entirely removed and that gallium nitride is removed from the portions of the lower layer superposed onto the portions 55a-b. The mask is subsequently removed by stripping. As illustrated in FIGS. 5a and 5b, grooves 60a-b are thus formed, whose respective depths pr are greater than the thickness et of the upper layer 25. The grooves each take the form of a strip, viewed in a direction normal n to the carrier, which extends over the entire length of the lower layer between two of its edges 65, 68 opposite to one another.

[0203] Thus, first thermoelectric members 70a-c of thermoelectric couples under formation are created, which respectively comprise parts 28a, 28b and 28c of the bilayer 28.

[0204] They each take, viewed in a direction normal n to the carrier, the form of a strip, and extend parallel to the adjacent grooves 60a-b.

[0205] The first thermoelectric members 70a-c are thus at a distance and electrically isolated from one another, the grooves having depths p.sub.r greater than the thickness e.sub.t of the upper layer, and extending from one side to the other between the edges 65 and 68. Thus, the interfaces 75a-c between the lower layer and the upper layer of each respective portion 28a-c of the bilayer 28, on which an electron gas can form and move, are electrically insulated from one another.

[0206] In the example illustrated, each groove has a length L.sub.r of 1.0 mm, a width l.sub.r of 2.06 μm and a depth p.sub.r of around 125 nm and each of the first thermoelectric members has a length L.sub.1th of 1.0 mm, identical to the length of a groove, a width l.sub.1th of 4.0 μm and a thickness, corresponding to the thickness of the doped portion 45, equal to 25 nm.

[0207] At the step c), an electrically-insulating coating is formed. An electrically-insulating material may be deposited, as illustrated in FIG. 6, on the top face of the upper layer 25 and on the respective bottom faces 90a-b of the grooves which are defined by the lower layer 20 of gallium nitride. A temporary layer 95 is thus formed. The electrically-insulating material is for example alumina and may be deposited by atomic layer deposition (ALD) or by chemical vapor deposition (CVD).

[0208] A mask 100 is subsequently generated by photolithography, the full portions 105 of the mask being totally superposed onto the groove, as illustrated in FIGS. 7a and 7b. The temporary layer is subsequently etched in its part or parts not covered by the full portions of the mask, as illustrated in FIG. 8. After stripping the full portions of the mask, electrically-insulating coatings 110a-b are formed, each entirely covering the lateral faces 115a-b,120a-b and the bottom face 125a-b of each of the grooves. Thus, each electrically-insulating coating extends across the whole width and over the entire length of the groove that it covers.

[0209] At the step d), in the example illustrated, a third material is deposited, for example a thermoelectric metal, in particular aluminum, on the top face of the bilayer and on the electrically-insulating coating, in such a manner as to form another temporary layer 130. Another mask 135 is subsequently formed by photolithography, whose full portions 140a-b completely cover the groove, as illustrated in FIG. 10.

[0210] After etching the other temporary layer and stripping the other mask, insertion layers 150a-b are formed, each of which entirely fills a corresponding groove. Each insertion layer protrudes from the bilayer 28. Furthermore, since the insertion layers are formed from a thermoelectric material, they each define second thermoelectric members 155a-b designed to form, with first corresponding thermoelectric members, thermoelectric couples 300a-b.

[0211] Each second thermoelectric member is thus contiguous with a first thermoelectric member. The electrically-insulating coating 110a-b forms a barrier between a first thermoelectric member and a second adjacent thermoelectric member, which are thus electrically isolated from one another, as illustrated in FIGS. 11a and 11b.

[0212] Furthermore, when observed in the direction n normal to the carrier, the first and second thermoelectric members each extend in directions of extension D.sub.E parallel to one another, and are aligned side by side in alternation in a direction of alignment D.sub.A perpendicular to the direction of extension D.sub.E. Two first and second adjacent thermoelectric members thus form a pattern 160 which is regularly repeated in the direction of alignment D.sub.A.

[0213] In one variant not illustrated, the third material may be a semiconductor and the method may comprise the doping of the insertion layer in order to endow it with thermo-electrical properties. In the example illustrated, the insertion layer may be of gallium nitride or of aluminum-gallium nitride and may be p-doped by implanting magnesium.

[0214] As described hereinabove, in the example illustrated, at the end of step d), the first thermoelectric members are electrically isolated from the second thermoelectric members by means of the electrically-insulating coating 110a-b. In order to form thermoelectric couples capable of generating a Seebeck effect, the method implemented in the example 1 comprises the deposition of a first layer of silica 180 which covers both the longitudinal end parts 185a-b, 190a-b of the first thermoelectric members and of the second thermoelectric members, respectively. As illustrated in FIGS. 12a and 12b, the first layer of silica extends from one side to the other over the upper layer 25 and over the insertion layers, in the direction of alignment D.sub.A. Viewed in the direction normal to the carrier, the first layer of silica thus takes the form of a rectilinear strip whose width lb is for example equal to 5.5 μm. Furthermore, the first layer of silica comprises first 195a-b and second 200a-b windows passing right through its thickness and which emerge onto the top face 205a-b of the first thermoelectric member and onto the top face 210a-b of the second thermoelectric member, respectively. Furthermore, the method comprises the formation of first 215a-b and second 220a-b electrically-conducting bump contacts, for example made of metal, and in particular of aluminum, which are accommodated within the windows. The windows, together with the electrically-conducting bump contacts, may be formed successively by a technique of lithography and etching such as described elsewhere in the present description.

[0215] Lastly, the method implemented in the example 1 comprises, as illustrated in FIGS. 13a and 13b, the formation of a second layer of silica 240 which is entirely superposed onto the first layer of silica 180 and vice versa. The second layer comprises another window 245a-b which passes right through its thickness and which emerges onto the first 220a-b and second 225 a-b electrically-conducting bump contacts. The other window is furthermore superposed onto the first layer of silica 180 and onto a first thermoelectric member 70a-b and onto a second adjacent thermoelectric member. An electrically-conducting strip 250a-b, for example of aluminum, is accommodated within the window and is in contact with the first and second electrically-conducting bump contacts. Thus, the electrically-conducting bump contacts and strip define an electrically-conducting bridge 260a-b which connects adjacent first 70a-b and second 155a-b thermoelectric members. Furthermore, the portion of the first layer of silica sandwiched between the electrically-conducting bridge and the thermoelectric members is an electrically-insulating spacer 270a-b.

[0216] The first and second thermoelectric members are thus electrically connected within an electrical connection region 280 extending over the longitudinal end portion over a length less than the width lb of the silica strip, and are electrically isolated from one another over an electrically-insulating region 290 which extends over the length of the groove. Thermoelectric couples 300a-b are thus created, which each comprises the first 70a-b and second 155a-b thermoelectric members respectively connected via the electrically-conducting bridge 260a-b, which under the effect of the heating of the transistor is capable of generating an electrical current by the Seebeck effect.

[0217] In order to increase the voltage generated by the sensor, the thermoelectric couples may be interconnected together in series. In conjunction with the formation of the first layer of silica 180, the method comprises the formation of another layer of silica 310 which covers the longitudinal end parts 320a-b, 330a-b of the first thermoelectric members and of the second thermoelectric members, respectively, opposite to the first layer of silica 180. Interconnection members of 340a-b connecting the second thermoelectric member, for example 155a of a thermoelectric couple, for example 300a, to the first thermoelectric member, for example 70b, of an adjacent thermoelectric couple, for example 300b, are formed according to a method identical to that described hereinabove for generating the electrically-conducting bridges.

[0218] A thermoelectric sensor 350, formed from thermoelectric couples electrically connected in series is thus obtained by means of the method implemented in the example 1.

[0219] It may be connected to a voltmeter or to an ammeter, by the means of connection lugs 352a-b deposited onto the carrier and to which it is connected, for measuring the electrical voltage or the electrical current respectively generated by an electronic unit 353, disposed on the carrier nearby, as illustrated in FIG. 14. For example, the separation distance d separating the electronic unit and the thermoelectric sensor may be in the range between 1 μm and 500 μm.

[0220] FIG. 14 illustrates an electronic component 356 comprising a thermoelectric sensor and an electronic unit 353 disposed on the carrier.

[0221] The electronic unit is for example a power transistor 355. It comprises, as the thermoelectric sensor 350, a stack 358 formed, consecutively and in contact one on top of the other, from: [0222] a primary layer 360 of aluminum nitride, [0223] a base layer 365 of gallium nitride, and [0224] an additional layer 370 of aluminum-gallium nitride.

[0225] The primary layers 15 and 360 preferably have the same thickness, the base layer 365 and lower layer 20 preferably have the same thickness and the additional layer 370 and upper layer 25 preferably have the same thickness.

[0226] The power transistor further comprises, on and in contact with the additional layer, a drain layer 375, a metal source layer 380, a layer for isolating the transistor 390 and a gate layer 400.

[0227] Preferably, the primary layer of the transistor, the base layer 365 and the additional layer are respectively formed during the same deposition steps as the primary layer, the lower layer and the upper layer of the thermoelectric sensor, respectively.

[0228] In other words, the method comprises the formation of the primary layer of the transistor, of the base layer and of the additional layer in conjunction with the deposition of the primary layer, the lower layer and the upper layer of the thermoelectric sensor, respectively.

[0229] Furthermore, the drain layer and the metal layer are preferably made of metal. They may be formed during the operation for deposition of the third material of the insertion layer of the thermoelectric sensor.

EXAMPLE 2

[0230] The thermoelectric sensor of the electronic component in the example 2, according to the invention, differs from that illustrated in the example 1 in that the first and second thermoelectric members of a thermoelectric couple are in direct contact with each other within an electrical connection region 370.

[0231] The thermoelectric sensor may be fabricated by implementing the steps a) and b) described hereinabove in order to form a groove.

[0232] As illustrated in FIG. 15, the method of fabrication differs from that implemented in the example 1 in that an electrically-insulating coating 110a-b is formed which partially covers only the faces of the groove. In order to form such a coating, a mask is deposited on the temporary layer 95, which is not superposed onto a portion of the groove in a longitudinal end portion 370a-b of the groove. In particular, in said longitudinal end portion, the electrically-insulating coating 110a covers the part of the groove contiguous with a portion 28b of the bilayer 28 destined to form a first thermoelectric member 70b of another adjacent thermoelectric couple. The formation of a short-circuit within the thermoelectric sensor is thus avoided.

[0233] The method subsequently comprises the formation of an insertion layer as described in the example 1, which entirely fills the volume of the groove. As illustrated in FIG. 16, the second thermoelectric member 155a-b thus formed is, in the end portion of the groove, in direct contact with an adjacent first thermoelectric member within an electrical connection region 375a-b and electrically isolated from the other adjacent first thermoelectric member. The electrical contact region may notably extend over a distance L.sub.z, measured along the length of the groove, of less than 10 μm. Furthermore, in the electrically-insulating region 380a-b, where the electrically-insulating coating completely covers the faces of the groove, the first and second thermoelectric members are at a distance from one another and electrically isolated, as already illustrated in FIG. 11a.

[0234] The method according to the second example is thus particularly simple to implement. The thermoelectric sensor may be fabricated with a limited number of layers to be deposited.

[0235] Furthermore, in order to interconnect two adjacent thermoelectric couples, the electrically-insulating coating is not superposed, in the opposite end portion 390a-b of the groove, onto the face of the groove 120a-b contiguous with the portion of the bilayer destined to form a first thermoelectric member of another thermoelectric couple. Thus, in the electrical interconnection region as illustrated in FIG. 17, the second thermoelectric member 155a of a thermoelectric couple 300a is in direct contact with the first thermoelectric member 70b of the adjacent thermoelectric couple 300b. The adjacent thermoelectric couples are thus connected in series.