Mems thermoelectric generator, corresponding manufacturing method and heating system

Abstract

The present disclosure relates to a MEMS thermoelectric generator, a corresponding manufacturing method and a heating system. The MEMS thermoelectric generator comprises: a thermoelectric unit comprising one or more thermoelectric elements partially extending over a cavity of the thermoelectric unit; a thermoplastic layer extending over the thermoelectric unit and having a top surface and a bottom surface opposite to each other along a first axis, the bottom surface facing the thermoelectric unit and the thermoplastic layer being made of a thermally insulating material and configured to be processed by a laser direct structuring, LDS, technique; a heat sink configured to exchange heat with the thermoelectric unit, the thermoelectric unit being interposed between the heat sink and the thermoplastic layer along the first axis; and a thermal via of a metallic material extending through the thermoplastic layer from the top surface to the bottom surface so that the thermal via overlaps the cavity along the first axis, wherein the thermoelectric unit can exchange heat with a heat source through the thermal via.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a MEMS thermoelectric generator. Furthermore, the present disclosure relates to a method of manufacturing the generator and to a heating system comprising the generator. In particular, the thermoelectric generator is of the MEMS type and comprises at least one thermoelectric cell and one thermoplastic layer extending over the thermoelectric cell; a thermal via extends through the thermoplastic layer and allows heat from an (external) heat source, which can be coupled to the MEMS thermoelectric generator, to propagate towards a portion of the thermoelectric cell. This allows an increase in the thermal drop between the opposite ends of one or more thermoelectric elements comprised in the thermoelectric cell. BACKGROUND

[0002] It is known that the direct conversion of thermal energy into electrical energy by the Seebeck effect is a promising method for harvesting energy from a heat source (thermal source). This is particularly useful in the field of MEMS ("Micro Electro Mechanical Systems") when dealing with small temperature gradients (e.g. lower than a few tens of °C, for example equal to about 40 °C), which would not be possible to exploit in any other way (e.g. from industrial plants, from car engines, low temperature thermal sources), precisely considering the small dimensions.

[0003] MEMS thermoelectric generators are MEMS devices for exploiting the waste heat from a thermal source, which are for example used in actuators of heater valves without cells or in torches (in the latter case, exploiting the temperature difference between the human body temperature and the ambient temperature).

[0004] Generally, thermoelectric generators use a thermoelectric material capable of generating electrical energy from the received heat, thus providing a potential difference (and therefore an electric current) from the temperature difference (thermal drop) between the two ends of the generator.

[0005] Generally, thermoelectric materials have a low electrical resistivity (p, for example lower than about 1 mΩ'cm) and a low thermal conductivity (K, for example lower than about 25 W'm －1 K －1 ). The low thermal conductivity ensures a high temperature difference between the end of the heated material and the opposite end of the material, even in the case of a thermal source that generates a small amount of heat. Furthermore, the voltage difference generated between these ends of the thermoelectric material is proportional to the relative temperature difference. Therefore, the low thermal conductivity ensures a high voltage difference even from a thermal source that generates a small amount of heat.

[0006] It is known that tellurium-based thermoelectric generators use a tellurium-based material as a thermoelectric material.

[0007] Tellurium compounds, such as bismuth telluride (Bi2Te3), have a good Seebeck coefficient (the Seebeck coefficient of a material, also known as thermoelectric power, thermoelectric sensitivity, is a measure of the magnitude of the thermoelectric voltage induced by the Seebeck effect in response to a temperature difference across the material), a high electrical conductivity and a low thermal conductivity (for example, the thermal conductivity of bismuth telluride is about 2 W'm－1 K －1 These properties make bismuth telluride suitable for forming the "thermoelectric active elements" of a thermoelectric generator ("thermoelectric active elements" or "active elements" refer to thermoelectric elements of thermoelectric material capable of converting a temperature gradient into an electric potential by the Seebeck effect).

[0008] A conventional tellurium-based thermoelectric generator comprises a plurality of N-doped bismuth telluride active elements and P-doped bismuth telluride active elements interconnected between a pair of opposite ceramic substrates provided with metal (Cu or Au) contact areas and wires interconnecting the N-doped bismuth telluride active elements and the P-doped bismuth telluride active elements to each other. The active elements are formed as discrete elements, typically by a process provided to form ingots from a powder material and subsequently cutting the ingots to form pellets which, when interposed between two ceramic substrates, define the active elements (for example, in a manual or semi-automatic assembly step).

[0009] Conventional tellurium-based thermoelectric generators are therefore discrete elements, thus bulky and not scalable. In more detail, bismuth telluride is not suitable as a material in the standard manufacturing processes of integrated circuits (ICs), which are based on silicon; in fact, although solutions are known to integrate bismuth telluride in MEMS devices, these solutions are not feasible in large-scale practice due to the lack of standardised manufacturing processes in MEMS technologies using bismuth telluride. Moreover, tellurium is a rather rare element, expensive and with strong environmental impact, which essentially limits its widespread use.

[0010] Silicon-based MEMS thermoelectric generators are also known, in which a silicon-based material (N-doped and P-doped so as to exhibit different Seebeck coefficients from each other) is used as a thermoelectric material to form the active elements. Silicon-based thermoelectric generators manufactured with MEMS technology compatible with silicon generally have a heat flow transverse or orthogonal to the substrate ("out-of-plane" heat flow) and comprise a plurality of thermoelectric cells having N-P doped active elements having a main extension direction transverse or orthogonal to the substrate and arranged in such a way that the thermoelectric cells are thermally parallel and electrically series and / or parallel to each other. This ensures maintaining a temperature difference sufficiently high to allow correct operation of these thermoelectric generators, but at the same time it makes them bulky (for example, the thickness of the active elements along the main extension direction is of the order of tens of pm). Moreover, the electric power generated by these thermoelectric generators is generally of the order of hundreds of pW, while some applications require higher electric power, for example of the order of mW. SUMMARY

[0011] A MEMS thermoelectric generator is provided, as well as a manufacturing process of the generator and a heating system comprising the generator.

[0012] A microelectromechanical system (MEMS) thermoelectric generator includes at least one thermoelectric unit, the thermoelectric unit comprising: a substrate of semiconductor material having a cavity between a first surface and a second surface of the substrate, the first surface and the second surface being opposite to each other along a first direction; an electrically insulating layer on the first surface of the substrate and above the cavity; and one or more thermoelectric elements in the electrically insulating layer; each of the one or more thermoelectric elements having a first end and a second end opposite to each other along a second direction transverse to the first direction, and configured to convert a heat drop between the first end and the second end into an electrical potential between the first end and the second end via the Seebeck effect, the first end of each thermoelectric element being above the cavity, and the second end of each thermoelectric element being above the substrate.

[0013] The MEMS thermoelectric generator further includes: a thermoplastic layer extending over the at least one thermoelectric element, the thermoplastic layer being made of a thermally insulating material and configured to be processed by laser direct forming technology; a heat sink coupled to a first end of the at least one thermoelectric element and configured to exchange heat with the thermoelectric element, the heat sink facing a first surface of the thermoplastic layer; and a thermal via of metallic material extending from the electrically insulating layer through the thermoplastic layer to the first surface of the thermoplastic layer, the thermal via being above the first end of each thermoelectric element. The MEMS thermoelectric generator is coupled to a heat source, the first surface of the thermoplastic layer facing the heat source, and the at least one thermoelectric element exchanging heat with the heat source through the thermal via to generate the heat drop between the first and second ends of each thermoelectric element. Attached Figure Description

[0014] To better understand this disclosure, preferred embodiments will now be described by way of non-limiting examples, in which:

[0015] Figure 1 A cross-section of an embodiment of a MEMS thermoelectric generator is shown;

[0016] Figure 2 An example is shown. Figure 1 A top view showing the thermoelectric unit of a MEMS thermoelectric generator with a portion removed;

[0017] Figure 3 It shows Figure 2 The cross-section of the thermoelectric unit;

[0018] Figure 4 It shows Figure 1 Another cross-section of the MEMS thermoelectric generator;

[0019] Figure 5A - Figure 5H A cross-section is shown according to the embodiment. Figure 2 The various manufacturing steps of the thermoelectric unit;

[0020] Figure 6A - Figure 6D A cross-section is shown according to the embodiment. Figure 1 The various manufacturing steps of a MEMS thermoelectric generator;

[0021] Figure 7 Cross sections of different embodiments of MEMS thermoelectric generators are shown;

[0022] Figure 8 It shows Figure 7 A perspective view of a MEMS thermoelectric generator;

[0023] Figure 9 and 10 Cross sections of corresponding and additional embodiments of the MEMS thermoelectric generator are shown;

[0024] Figure 11A - Figure 11B A cross-section is shown according to the embodiment. Figure 10 The various manufacturing steps of a MEMS thermoelectric generator;

[0025] Figure 12 This is a schematic diagram of a heating system that includes a MEMS thermoelectric generator;

[0026] Figure 13 Cross sections of different embodiments of the thermoelectric unit are shown;

[0027] Figure 14 It shows Figure 13 A top view of the removed parts of the thermoelectric unit.

[0028] In particular, the accompanying drawings are illustrated with reference to a three-axis Cartesian system defined by the X-axis, Y-axis, and Z-axis, which are transverse to each other and, more specifically, orthogonal to each other. Detailed Implementation

[0029] In the following description, elements common to different embodiments are indicated by the same reference numerals.

[0030] Figure 1 An embodiment of a MEMS thermoelectric generator 10 is shown, which can be connected to a heat source 12 during use, such that it exchanges heat with the heat source 12 through conduction, so that the heat received from the heat source 12 generates electrical power. In particular, Figure 1 The figure shows a cross-section of the MEMS thermoelectric generator 10 in the XZ plane defined by the X and Z axes.

[0031] The MEMS thermoelectric generator 10 (hereinafter also simply referred to as generator 10) comprises one or more thermoelectric units 100. Figure 1 A single thermoelectric unit 100 is exemplarily shown, however it is clear that a plurality of thermoelectric units 100 can be present similarly. In case of more thermoelectric units 100, they are arranged so that they are thermally in parallel and electrically in series and / or in parallel (e.g. when there are more groups of thermoelectric units 100 in parallel to each other, each group comprising thermoelectric units 100 in series to each other, a combination of series and parallel arrangement occurs).

[0032] With reference to Figure 2 and Figure 3 The thermoelectric unit 100 is described in more detail, Figure 2 and Figure 3 A top view (in the XY plane defined by the X and Y axes) and a cross-sectional view (in the XZ plane) of an embodiment of the thermoelectric unit 100 are respectively shown. In particular, Figure 3 A cross-sectional view of the thermoelectric unit 100 along the section line I-I is shown. Figure 2

[0033] In detail, the thermoelectric unit 100 comprises a substrate 105 of a semiconducting material, such as silicon. The substrate 105 has a first surface 105a and a second surface 105b opposite each other along the Z axis.

[0034] A cavity 115 extends through the substrate 105 from the first surface 105a to the second surface 105b. In Figure 3 In cross-section, the cavity 115 is laterally delimited (i.e. along the X axis) by first and second portions 105L and 105R of the substrate 105. In other words, the cavity 115 extends along the X axis between the first and second portions 105L and 105R.

[0035] The thermoelectric unit 100 comprises, on the first surface 105A of the substrate 105, a bottom electrically insulating layer 120, for example made of an electrically insulating material such as an oxide (e.g. silicon oxide). The bottom electrically insulating layer 120 also extends over the cavity 115, so that the bottom electrically insulating layer 120 overhangs the cavity 115.

[0036] The thermoelectric unit 100 further comprises one or more thermoelectric elements 110 configured to convert a thermal drop across the thermoelectric element 110 into an electric potential by the Seebeck effect. The thermoelectric element 110 is made of a thermoelectric material, in particular of poly-Si or poly-SiGe. The thermoelectric element 110 extends over the bottom electrically insulating layer 120.

[0037] ​In detail, the thermoelectric element 110 comprises a plurality of interconnected thermoelectric microstructures. Each thermoelectric microstructure has a main extension direction transverse or perpendicular to the Z axis, and is here exemplarily considered parallel to the X axis. In particular, the thermoelectric microstructures comprise a plurality of thermoelectric microstructures having N-type conductivity (hereinafter referred to as N-type thermoelectric microstructures 110N) and a plurality of thermoelectric microstructures having P-type conductivity (hereinafter referred to as P-type thermoelectric microstructures 110P). In more detail, the N-type thermoelectric microstructures 110N are N-doped (e.g. with phosphorus) polycrystalline Si (or polycrystalline SiGe) thermoelectric microstructures, and the P-type thermoelectric microstructures 110P are P-doped (e.g. with boron) polycrystalline Si (or polycrystalline SiGe) thermoelectric microstructures. In detail, the thermoelectric microstructures 110N, 110P exhibit a thermal conductivity of about 5 W / mK －1 －1 to about 25 W / mK －1 －1 .

[0038] As can be better understood in Figure 2 , the N-type thermoelectric microstructures 110N and the P-type thermoelectric microstructures 110P are electrically connected in series to each other in an alternating manner through respective electrically conductive elements 125 (e.g. made of a metallic material such as Al, Ag, Au or Cu); in other words, each N-type thermoelectric microstructure 110N is electrically connected in series to a subsequent P-type thermoelectric microstructure 110P through a respective electrically conductive element 125, and to a respective preceding P-type thermoelectric microstructure 110P through a respective electrically conductive element 125. In particular, the N-type thermoelectric microstructures 110N and the P-type thermoelectric microstructures 110P alternate each other along the Y axis, and each of them has a main extension direction parallel to the X axis. Each thermoelectric microstructure 110N and 110P has a first end 110' and a second end 110" opposite each other along the respective main extension direction (i.e. opposite each other along the X axis). Each end 110' and 110" is in electrical contact with a respective electrically conductive element 125; for example, the electrically conductive elements 125 extend on the respective first or second end 110', 110". Moreover, in use, the ends 110' and 110" are at different temperatures, so that there is a temperature difference between them (in detail, T' > T", where T' is the temperature of the first end 110' and T" is the temperature of the second end 110"). Therefore, the heat flow through the thermoelectric microstructures 110N and 110P is planar (i.e. it is transverse or orthogonal to the Z axis).

[0039] ​​Furthermore, each N-type thermoelectric microstructure 110N and P-type thermoelectric microstructure 110P partially vertically overlap (i.e., along the Z-axis) on the substrate 105 and partially vertically overlap on the cavity 115. In detail, a first end 110' of each thermoelectric microstructure 110N, 110P vertically overlaps on the cavity 115 and a second end 110" of each thermoelectric microstructure 110N, 110P vertically overlaps on the substrate 105. This ensures a temperature difference between the ends 110' and 110". Indeed, there is air or vacuum inside the cavity 115, which has a much lower thermal conductivity, for example 500 to 1000 (e.g., 700) factors lower than the thermal conductivity of the substrate 105. Therefore, the heat generated by the heat source 12 and provided to the thermoelectric cell 100 at the first end 110' (as better described below) is mainly radiated through the thermoelectric microstructures 110N, 110P (having a higher thermal conductivity than the bottom electrically insulating layer 120) and then towards the second surface 105b through the substrate 105. In other words, the cavity 115 is thermally operated as an open circuit, which prevents the heat from being directly radiated from the first end 110' to the substrate 105 through the bottom electrically insulating layer 120 (i.e., in a substantially vertical manner along the Z-axis and thus with an out-of-plane heat flow), and relatively forces the heat to be transferred through the entire length of the thermoelectric microstructures 110N, 110P before reaching the substrate 105 (i.e., substantially along the X-axis at the thermoelectric microstructures 110N, 110P and the bottom electrically insulating layer 120 and thus with an in-plane heat flow).

[0040] For example, the N-type thermoelectric microstructures 110N and the P-type thermoelectric microstructures 110P are formed on the bottom electrically insulating layer 120 according to a planar serpentine arrangement. An example of such an arrangement is described in M. Tomita et al. "10 μW / cm2-Class High Power Density Planar Si-Nanowire Thermoelectric Energy Harvester Compatible with CMOS-VLSI Technology." In detail, the thermoelectric microstructures 110N and 110P can comprise at least two groups of thermoelectric microstructures, each group comprising N-type thermoelectric microstructures 110N and P-type thermoelectric microstructures 110P arranged serpentine to each other along the Y-axis and alternating, and these groups are arranged laterally to each other along the X-axis to form a single serpentine arrangement, and so that the ends of the thermoelectric microstructures 110N and 110P of different groups facing each other are at the same temperature in use (at the same temperature as the substrate 105 in the example of Figure 2 and Figure 3 In the example of Figs. 1 and 2, the first ends 110' of the thermoelectric microstructures 110N and 110P of the two groups shown face each other).

[0041] Since the N-type thermoelectric microstructure 110N and the P-type thermoelectric microstructure 110P have opposite conduction types, they also have opposite Seebeck coefficients: when the heat source 12 is coupled to the thermoelectric cell 100, as better described below, a temperature gradient (thermal drop) is established between the ends 110' and 110" of the thermoelectric microstructures 110N, 110P (in fact, the thermoelectric microstructures 110N, 110P are placed between the heat source 12 and the substrate 105, which in turn is coupled to a heat sink, as better described below), which, by the Seebeck effect, generates a corresponding potential difference (voltage difference or voltage drop) between the ends 110' and 110" of each thermoelectric microstructure 110N, 110P, so, considering the serpentine arrangement, a total potential difference is induced between the conductive terminals 132 placed at the ends of the serpentine arrangement (the total potential difference is equal to the sum of the potential differences between the ends 110' and 110" of each thermoelectric microstructure 110N, 110P, and is caused by the flow of charge carriers within the thermoelectric microstructures 110N, 110P driven by the temperature gradient).

[0042] In addition, in a manner not shown in Figure 2 and Figure 3 but shown in Figure 1 , the thermoelectric cell 100 also comprises a top electrically insulating layer 130, for example made of an insulating material such as an oxide (for example, silicon oxide), which extends on the thermoelectric elements 110 and on the areas of the bottom electrically insulating layer 120 not covered by the thermoelectric elements 110. In addition, the top electrically insulating layer 130 extends on the conductive elements 125, so that the conductive elements 125 placed on the first ends 110' of the thermoelectric microstructures 110N, 110P (hereinafter, first conductive elements 125') and the conductive elements 125 placed on the second ends 110" of the thermoelectric microstructures 110N, 110P (hereinafter, second conductive elements 125") are covered and at least partially leave exposed the conductive terminals 132 (for example, Figure 4 ). In this way, the top electrically insulating layer 130 electrically insulates the thermoelectric microstructures 110N, 110P, 110P, but also allows their electrical connection towards the external environment through the conductive terminals 132, as better described below.

[0043] More generally, the top electrically insulating layer 130 and the bottom electrically insulating layer 120 form an electrically insulating layer 120, 130 in which the thermoelectric microstructures 110N, 110P and the conductive elements 125 are buried and the conductive terminals 132 are at least partially exposed in relation.

[0044] Again with reference to Figure 1The generator 10 also includes a heat sink 14 (e.g., a metal plate of a thermally conductive material such as aluminum, optionally including heat sink fins to increase heat dissipation to the external environment) thermally coupled to the substrate 105. For example, the second surface 105b of the substrate 105 is secured to the die pad (made of a conductive material such as copper) 16 by an adhesive layer 18 (e.g., a “conductive die attachment film” CDAF type) inserted along the Z-axis between the substrate 105 and the die pad 16; furthermore, the die pad 16 is secured to the heat sink 14 and extends, for example, on the heat sink 14 such that it is inserted along the Z-axis between the heat sink 14 and the substrate 105. The adhesive layer 18 and the die pad 16 are thermally conductive, allowing heat transfer from the substrate 105 to the heat sink 14.

[0045] The generator 10 also includes a thermoplastic layer (or total thermoplastic layer) configured to be processed (i.e., manipulated) by a known type of "laser direct forming" (LDS) technology. In this embodiment, the thermoplastic layer is formed from a first thermoplastic layer. Figure 1 The first thermoplastic layer 20 is indicated by reference numeral 20 in the accompanying drawings. Specifically, the first thermoplastic layer 20 is doped with an organometallic compound (e.g., a metal such as palladium, Pd). 2+ Or copper, Cu 2+ The thermoplastic polymer material containing chelated complexes: When the laser beam irradiates the first thermoplastic layer 20, the organometallic compounds present in the irradiated polymer material are chemically activated, enabling them to selectively precipitate metals via electroplating catalysis in subsequent metal deposition steps, as better described below. More details regarding the material of the first thermoplastic layer 20 and the LDS technology can be found in the literature “Manufacturing of Molded Interconnect Devices from Prototyping to Mass Production with LaserDirect Structuring”, Heininger et al., 2004. Furthermore, the thermoplastic polymer material is chosen to have a reduced thermal conductivity, particularly below approximately 1 W·m. －1 〃K －1 For example, thermoplastic polymers can be epoxy resins.

[0046] A first thermoplastic layer 20 covers the thermoelectric unit 100 to thermally insulate it from the heat source 12. In particular, the first thermoplastic layer 20 extends over the thermoelectric unit 100 (i.e. on the top surface 130a of the top electrically insulating layer 130, opposite the bottom electrically insulating layer 120 along the Z axis), and also extends laterally to the thermoelectric unit 100, and over the exposed areas of the die pad 16 and of the heat sink 14, so that the thermoelectric unit 100 is encapsulated between the first thermoplastic layer 20 and the die pad 16. In more detail, the first thermoplastic layer 20 has a top surface 20a and a bottom surface 20b opposite each other along the Z axis, wherein the bottom surface 20b is in contact with the thermoelectric unit 100, the die pad 16 and the heat sink 14.

[0047] A thermal via (or thermal connection, or total thermal via) of thermally conductive material (e.g. metal, e.g. copper) extends through the first thermoplastic layer 20 so that it faces (and optionally protrudes beyond) the top surface 20a and is in contact with the thermoelectric unit 100 at the first end 110' of the thermoelectric microstructure 110N, 110P. In the present embodiment, the thermal via is formed by a first thermal via 30. In detail, the first thermal via 30 extends from the top surface 20a to the bottom surface 20b along the Z axis so that it is in contact with the top surface 130a of the top electrically insulating layer 130 and vertically (along the Z axis) superimposed on the first electrically conductive element 125'. The first thermal via 30 has a first end 30' and a second end 30" opposite each other along the Z axis, the first end 30' protruding outside the first thermoplastic layer 20 at the top surface 20a (or more generally, facing the top surface 20a), the second end 30' being in contact with the top surface 130a of the top electrically insulating layer 130 and aligned with the first electrically conductive element 125' along the Z axis. In detail, the second end 30" extends only on the first end 110' and on the area comprised between the first end 110' and the second end 30', so that it forces the flow of heat to flow through the thermoelectric microstructure 110N, 110P, thus preventing it from occurring in a substantially vertical manner; in more detail, the first end 110' refers to a portion of the length of the thermoelectric microstructure 110N, 110P along the X axis at most equal to about 20% of the maximum total length of the thermoelectric microstructure 110N, 110P. Thanks to the top electrically insulating layer 130 interposed between the first thermal via 30 and the first electrically conductive element 125' along the Z axis, the first electrically conductive element 125' is electrically insulated with respect to the first thermal via 30; however, they exchange heat with the first thermal via 30 by conduction, since the top electrically insulating layer 130 is a thermally conductive material (or in any case has a thickness along the Z axis such that it creates a reduced thermal resistance, e.g. lower than about 0.15 Ω).

[0048] In particular and as better described below, the first thermal via 30 is provided in the first thermoplastic layer 20 by LDS, i.e. by laser ablation and activation of portions of the first thermoplastic layer 20, followed by electroplating in the active area.

[0049] For illustrative and non-limiting purposes, the first thermal via 30 has a substantially cylindrical or conical shape (thus, the XY plane section is constant from the first end 30' to the second end 30", or respectively decreases from the first end 30' to the second end 30",) or the cylindrical / conical shape is tapered centrally along the Z axis (as shown in Figure 1 indicated, where the ends 30' and 30" are connected to each other by a central portion integral with the ends 30' and 30" and with XY plane sections lower than the XY plane sections of the ends 30' and 30"). In particular, the second shape ensures a greater area in contact with the heat source 12 and with the thermoelectric unit 100, while keeping the section of the central portion of the first thermal via 30 limited, thus optimizing the heat exchange of the first thermal via 30 without compromising its manufacturability by LDS.

[0050] Optionally, a thermally conductive material, for example a metal, thermal coupling layer 32 (for example, comprising a stack of metal layers, which in turn comprise, for example, Sn-Cu-Ni-Au in succession to each other) externally surrounds the first end 30', so that it allows the heat exchange between the first thermal via 30 and the external environment (for example, the heat source 12) and prevents the oxidation of the first end 30' of the first thermal via 30.

[0051] Figure 4 The generator 10 is shown along the cross-sectional line IV-IV, indicated. Figure 2 The generator 10 is shown along the cross-sectional line IV-IV, indicated.

[0052] As shown in Figure 4 indicated, each conductive terminal 132 is electrically connected to a respective lead 45 by a respective electrical connection structure 40. The leads 45 and the electrical connection structures 40 are included in the generator 10 and are optional. For example, the leads 45 extend on the heat sink 14 (so that they are electrically insulated with respect to the heat sink 14, for example by an electrically insulating layer 60 described below), extend transversely to the die pads 16, and extend with respect to the die pads 16 on opposite sides of each other along the X axis, so that they are surrounded by the first thermoplastic layer 20 and by the heat sink 14. The leads 45 form, together with the die pads 16, a frame of the generator 10.

[0053] In Figure 4In this embodiment, each electrical connection structure 40 includes a first through-hole 41, a second through-hole 42, and an electrical connection portion 43 connecting the through-holes 41 and 42. The first and second through-holes 41 and 42 are similar to the first thermal through-hole 30 and therefore will not be described in detail. The first through-hole 41 extends from the top surface 20a through the first thermoplastic layer 20 to the thermoelectric unit 100, such that it makes electrical contact with a corresponding conductive terminal 132. The second through-hole 42 extends from the top surface 20a through the first thermoplastic layer 20 to a corresponding lead 45, such that it makes electrical contact with the latter. The electrical connection portion 43 has the same material as the through-holes 41 and 42 and extends on the top surface 20a between the through-holes 41 and 42, such that the electrical connection portion 43 makes the through-holes 41 and 42 make electrical contact with each other. Furthermore, an insulating layer 44 of insulating material, such as oxide (e.g., insulating tape with a thickness of a few μm along the Z-axis), surrounds the electrical connection portion 43 externally, thereby making the electrical connection structure 40 electrically and thermally insulated relative to the external environment. In this way, a conductive path is created between the conductive terminal 132 and the corresponding lead 45, thereby allowing the potential difference generated by the thermoelectric unit 100 to be transferred to the lead 45.

[0054] Figure 5A - Figure 5H It shows Figure 2 and Figure 3 The various steps of the known manufacturing process of the thermoelectric unit 100 are described. Specifically, the manufacturing steps are shown with reference to a cross-section of the thermoelectric unit 100 taken along section line I-I.

[0055] exist Figure 5A In this embodiment, a substrate 105 (i.e., a first wafer of semiconductor material (e.g., Si) is disposed, and a bottom electrically insulating layer 120 (made of an electrically insulating material (e.g., oxide, such as silicon oxide)) and a thermoelectric material layer 204 (specifically, made of, for example, intrinsic polycrystalline silicon (poly-Si) or polycrystalline silicon-germanium (poly-SiGe)) are sequentially formed on its outer surface. Specifically, the substrate 105 has first and second surfaces 105a and 105b opposite to each other along the Z-axis, forming a portion of the outer surface of the substrate 105. Specifically, at the first surface 105a, the bottom electrically insulating layer 120 is formed on the substrate 105 (e.g., by thermal oxidation of the substrate 105), and the thermoelectric material layer 204 is formed on the bottom electrically insulating layer 120 (e.g., by deposition). The thermoelectric material layer 204 is used to form a thermoelectric element 110.

[0056] exist Figure 5BIn this process, a first doped portion 206N is provided in the thermoelectric material layer 204 by N-type doping of the first exposed region 204N. Specifically, a first mask 208 is formed on the thermoelectric material layer 204, covering the thermoelectric material layer 204, thereby exposing the first exposed region 204N; selective doping using an N-type dopant is performed in this first exposed region 204N in a manner known per se (e.g., by ion implantation); thereafter, the first mask 208 is removed. The first doped portion 206N is used to form the corresponding N-type thermoelectric microstructure 110N.

[0057] exist Figure 5C In this process, a second doped portion 206P is formed in the thermoelectric material layer 204 laterally to the first doped portion 206N through p-type doping of the second exposed region 204P. Specifically, a second mask 210 is formed on the thermoelectric material layer 204, covering the thermoelectric material layer 204 (specifically, the first doped portion 206N), thereby exposing the second exposed region 204P; selective doping using a p-type dopant is performed in this second exposed region 204P in a manner known per se (e.g., by ion implantation); thereafter, the second mask 210 is removed. The second doped portion 206P is used to form the corresponding p-type thermoelectric microstructure 110P.

[0058] exist Figure 5D In this process, the thermoelectric material layer 204 is removed (e.g., by etching such as dry etching) to expose the bottom electrical insulating layer 120, leaving first and second doped portions 206N and 206P on the bottom electrical insulating layer 120, which thus define corresponding N-type and P-type thermoelectric microstructures 110N, 110P. This etching is performed, for example, through another mask (not shown) that covers the first doped portion 206N and the second doped portion 206P, exposing the remainder of the thermoelectric material layer 204.

[0059] exist Figure 5E In this process, a protective oxide layer 212 (optionally, an oxide such as silicon oxide) is formed on the thermoelectric material layer 204 (e.g., by thermal oxidation of polycrystalline Si or polycrystalline SiGe). Furthermore, a first insulating layer 129 (part of the top electrical insulating layer 130) made of an insulating material such as BPSG (borophosphosilicate glass) is formed on the thermoelectric material layer 204 and on the N-type and P-type thermoelectric microstructures 110N, 110P. This occurs, for example, by depositing an insulating material on the thermoelectric material layer 204 and on the N-type and P-type thermoelectric microstructures 110N, 110P, followed by reflowing the deposited insulating material.

[0060] exist Figure 5FIn the N-type and P-type thermoelectric microstructures 110N, 110P, electrically conductive elements 125 (and similar electrically conductive terminals 132, not visible in the figure taken along the section line I-I) are provided. In particular, the etching of the first insulating layer 129 is performed at the ends 110' and 110" of the thermoelectric microstructures 110N, 110P so as to expose these ends 110' and 110" (e.g. this etching is performed through a further mask, not shown, previously formed on the thermoelectric material layer 204 so as to expose the areas of the latter vertically superimposed along the Z axis on the ends 110' and 110"); subsequently, the electrically conductive elements 125 are formed by depositing a metal (e.g. aluminium) at the exposed ends 110' and 110" of the thermoelectric microstructures 110N, 110P so that the electrically conductive elements 125 are in direct electrical and physical contact with the ends 110' and 110" of the thermoelectric microstructures 110N, 110P.

[0061] In a manner not shown, further deposition steps of one or more second insulating layers (e.g. of tetraethyl orthosilicate (TEOS)) and / or of passivation material (e.g. SiN) of electrically insulating material are performed on the first insulating layer 129 and on the electrically conductive elements 125, one after the other. These one or more second insulating layers, together with the first insulating layer 129, form a top electrically insulating layer 130 which covers the electrically conductive elements 125 and the thermoelectric microstructures 110N, 110P and exposes the electrically conductive terminals 132.

[0062] Furthermore, optionally and in a manner not shown, portions of an electrically conductive layer (made of a metal such as copper, hereinafter referred to as metal contact) are formed on the top electrically insulating layer 130 laterally to each other along the X axis, for forming the second ends 30" of the first thermal vias 30 and of the first and second electrical vias 41 and 42, and in the Figure 4 In particular, this occurs by etching away portions of the top electrically insulating layer 130 superimposed on the electrically conductive terminals 132 to form in the top electrically insulating layer 130 respective recesses (not shown) which expose the electrically conductive terminals 132 (in the case where the electrically conductive terminals 132 are already exposed by the top electrically insulating layer 130, this step is not present, e.g. as in the case of the embodiment of the first thermal via 30 of figure 2). Figure 4As shown), a conductive layer is then deposited on the region of the top electrical insulating layer 130 vertically superimposed on the first conductive element 125', and in the recesses formed in the top electrical insulating layer 130 (or in any case on the first conductive element 125' exposed by the top electrical insulating layer 130), and optionally also on the region of the top electrical insulating layer 130 adjacent to the recesses. The portions of the conductive layers (metal contacts) 33a and 33b thus provided are physically and electrically separated from each other. The metal contact 33a superimposed on the first conductive element 125' forms the second end 30″ of the first thermal via 30 and is electrically decoupled from the first conductive element 125' due to the top electrical insulating layer 130, while the metal contact 33b superimposed on the conductive terminal 132 forms the second end 30″ of the electrical via 41 and is coupled to the conductive terminal 132 through the recesses in the top electrical insulating layer 130 (therefore, these metal contacts 33b form conductive vias through the top electrical insulating layer 130).

[0063] Figure 5A - Figure 5F The steps result in the formation of thermoelectric unit 100, in which substrate 105 does not yet have cavity 115.

[0064] exist Figure 5G In this process, a second wafer (or transport wafer) 216 of semiconductor material (e.g., Si) is temporarily coupled (specifically, fixed) to the thermoelectric unit 100 such that it faces the top electrical insulating layer 130. For example, the second wafer 216 is bonded to the thermoelectric unit 100 by known wafer bonding techniques, such as by a bonding adhesive layer 218 interposed between the second wafer 216 and the top electrical insulating layer 130.

[0065] exist Figure 5HIn particular, a further mask (not shown) is formed on the second surface 105b so that it covers the second surface 105b leaving an exposed relative cavity area 220 through which the etching (e.g. dry etching such as by Bosch etching) is performed, which removes a portion of the substrate 105 along the Z-axis in alignment with the cavity area 220 of the second surface 105b exposed by the mask, thereby forming the cavity 115 separating the first and second portions 105L, 105R of the substrate 105 from each other along the X-axis. In detail, the cavity area 220 is aligned along the Z-axis with the first end 110' of the thermoelectric microstructure 110.

[0066] Subsequently, the second wafer 216 and the bonding adhesive layer 218 are removed to obtain a thermoelectric unit 100 of Figure 3 .

[0067] Figure 6A - Figure 6D The manufacturing process of the generator 10 of Figure 1 and Figure 4 is shown in various steps. In particular, the manufacturing steps are shown with reference to a cross-section of the generator 10 taken along the section line IV-IV and with reference to the rear end of the generator 10.

[0068] Figure 6A The thermoelectric unit 100 provided according to the steps discussed with reference to Figure 5A - Figure 5H is shown. Also shown are the metal contacts 33a and 33b which are not present in Figure 5A - Figure 5H With reference to Figure 6A , the thermoelectric unit 100 is fixed to the die pad 16 by means of the adhesive layer 18. Furthermore, the die pad 16 and the leads 45 are fixed to the heat sink 14, e.g. by means of known die attachment techniques. Moreover, a first thermoplastic layer 20 is formed on the thermoelectric unit 100 and the leads 45. In particular, the first thermoplastic layer 20 is formed by injection molding so that it covers the thermoelectric unit 100, the leads 45 and the heat sink 14 (in detail, so that it also extends between the leads 45 and the thermoelectric unit 100).

[0069] In Figure 6BIn the first thermoplastic layer 20, first trenches 140 are provided vertically superimposed on the metal contacts 33a and on the cavities 115, second trenches 141 (optional) are provided vertically superimposed on the respective metal contacts 33b and on the respective conductive terminals 132, and third trenches 142 (optional) are provided vertically superimposed on the respective leads 45. The trenches 140-142 are thus arranged laterally to each other and extend from the top surface 20a up to the bottom surface 20b, so as to expose the metal contacts 33a, the metal contacts 33b and the leads 45, respectively. The trenches 140-142 are provided by means of the LDS technique, i.e. by means of a laser beam that generates photochemical ablation and evaporation radiation of the polymeric material. In detail, the laser beam impinges on the respective trench areas of the top surface 20a of the first thermoplastic layer 20, causing ablation and evaporation of the polymeric material in these trench areas and thus forming the trenches 140-142. The trench areas are thus vertically superimposed on the metal contacts 33a (more generally, on the cavities 115), on the metal contacts 33b and on the leads 45, respectively. For example, the laser beam can be generated with a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser (for example, having a wavelength λ of about 1064 nm). In addition to selectively removing the radiated polymeric material, the laser beam also chemically activates the organic metal compounds contained in the polymeric material that is radiated but not removed. In more detail, when the polymeric material is radiated for a time longer than a threshold value (in a manner known per se, depending on factors such as the chosen polymeric material and the wavelength of the laser beam), it is evaporated and separates from the first thermoplastic layer 20; on the other hand, when the radiation time is shorter than the threshold value, the polymeric material does not detach from the first thermoplastic layer 20 and the organic metal compounds contained therein are chemically modified so that they become selective catalysts for the deposition of metals. For this purpose, the side walls 140', 141', 142' of the trenches 140, 141, 142 are chemically activated by the laser beam during the formation of the trenches 140, 141, 142. Further details regarding the LDS technique can be found in the document "Manufacturing of Molded Interconnect Devices from Prototyping to Mass Production with Laser Direct Structuring", Heininger et al., 2004.

[0070] In Figure 6CIn particular, there are irradiated and activated: a first activation region 140" (optional) of the top surface 20a, which surrounds the opening of the first trench 140 and is intended to house the first end 30' of the first thermal via 30; a second activation region 141" (optional) of the top surface 20a, which surrounds the opening of the respective second trench 141 and is intended to house the first end 30' of the first electrical via 41; a third activation region 142" (optional) of the top surface 20a, which surrounds the opening of the respective third trench 142 and is intended to house the first end 30' of the second electrical via 42; a fourth activation region 143 of the top surface 20a, which extends along the X axis between the respective second and third activation regions 142' and 142" (more generally, between the respective second and third trenches 141 and 142) and is intended to house the electrical connection portion 43.

[0071] In Figure 6D In particular, metal (for example, Cu) is deposited in the trenches 140-142 and on the top surface 20a of the first thermoplastic layer 20. The metal deposition adheres to the first thermoplastic layer 20, which has been chemically activated by the laser beam, so that it catalyzes the metal precipitation. Thus, the metal is deposited in the trenches 140-142 (up to reaching and electrically and physically contacting the metal contacts 33a and 33b and the lead 45) and on the activation regions 140"-142", 143. Thus, the generator 10, which has the first thermal via 30 and the electrical connection structure 40 arranged in the first thermoplastic layer 20, defines a Molded Interconnect Device (MID).

[0072] Then, in an optional and not shown manner, a thermal coupling layer 32 is formed on the first end 30' of the first thermal via 30. In particular, this occurs by electroplating the growth of one or more metal layers (for example, Sn-Cu-Ni-Au, consecutive to each other) on the first end 30' of the first thermal via 30 (of an electrically conductive material, such as copper).

[0073] Moreover, again in an optional and not shown manner, the formation of an insulating layer 44 is performed on the electrical connection portion 43. In particular, this occurs by gluing an insulating tape on the electrical connection portion 43. By the aforementioned steps, the structure of the generator 10 shown is obtained. Figure 4

[0074] Figure 7 Different embodiments of the generator 10 are shown. In particular, Figure 7 The generator 10 of Figure 4 ​generator of the type described above, and therefore will not be described in detail.

[0075] However, in Figure 7 In the embodiment of the generator 10, a second thermoplastic layer 48 extends over the aforementioned first thermoplastic layer 20 and over the electrical connection structure 40. The second thermoplastic layer 48 is similar to the first thermoplastic layer 20 and is integral with the first thermoplastic layer 20. In this embodiment, a thermoplastic layer, here indicated with reference 52, is formed by the first thermoplastic layer 20 and the second thermoplastic layer 48 and has a top surface 52a (facing the heat source 12 in use) and a bottom surface 52b (coinciding with the bottom surface 20b of the first thermoplastic layer 20).

[0076] Furthermore, Figure 7 The generator 10 of the type described above comprises a second thermal via 50 over the first thermal via 30. In this embodiment, a thermal via is formed by the first and second thermal vias 30, 50 and is also indicated with reference 54. Similarly to the first thermal via 30, the second thermal via 50 vertically overlaps the first thermal via 30 and is in direct physical contact with the latter. In particular, the first end 30' of the first thermal via 30 acts as a second end 50" of the second thermal via 50, while the first end 50' of the second thermal via 50 faces (optionally protrudes beyond) the top surface 52a. The thermal via 54 crosses the thermoplastic layer 52 from the top surface 52a (first end 50') up to the top electrically insulating layer 130 (second end 30") of the thermoelectric cell 100. The heat source 12 can be coupled to the first end 50' of the second thermal via 50 so that it allows the heat exchange between the heat source 12 and the thermoelectric cell 100 through the thermal via 54.

[0077] Generally, in Figure 7 In this embodiment, the electrical connection structure 40 is buried in the thermoplastic layer 52; on the other hand, the first end 50' of the thermal via 54 extends on the top surface 52a so that it can be in contact with the heat source 12 to receive heat from the heat source 12. In more detail, the thermoplastic layer 52 surrounds the electrical connection structure 40 and also extends over the electrical connection portion 43, in particular having a thickness along the Z axis, so that it prevents the heat exchange between the electrical connection structure 40 and the external environment. In this way, the electrical connection structure 40 is thermally insulated with respect to the heat source 12 by the thermoplastic layer 52. Therefore, the heat source 12 can be in contact with the thermal via 54 and the top surface 52a to exchange heat with the thermal via 54, while ensuring the thermal insulation of the electrical connection structure 40. In addition, in Figure 4 In the embodiment of the type described above, the thermal and electrical insulation of the electrical connection structure 40 is ensured by the insulating layer 44.

[0078] Furthermore, Figure 7An electrically insulating layer 60 (optional) is also shown interposed along the Z-axis between the heat sink 14 and the lead 45. Optionally, the electrically insulating layer 60 is also interposed along the Z-axis between the heat sink 14 and the die pad 16. The electrically insulating layer 60 fixes the lead 45 and the die pad 16 to the heat sink fin 14 and is made of an electrically insulating material but not of a thermally insulating material (e.g., made of a silicone-based material, such as a thermal interface material, TIM). In this way, the electrically insulating layer 60 allows the heat exchange between the die pad 16 and the heat sink fin 14 and electrically decouples both the lead 45 and the die pad 16 with respect to the heat sink fin 14, thus making the operation of the generator 10 independent from any noise or electrical interference caused by the external environment on the heat sink fin 14. Although the electrically insulating layer 60 is shown with reference to the only embodiment of the generator 10 described above with reference to Figure 7 , it can similarly be present in the other embodiments of the generator 10.

[0079] Figure 7 The generator 10 of this embodiment is manufactured using the manufacturing process previously described with reference to Figure 5A . Figure 5H and Figure 6A . Figure 6D Moreover, the manufacturing process according to this embodiment comprises, at the end of the formation of the first thermal via 30 and of the electrical connection structure 40 (i.e., before the formation of the thermal coupling layer 32 and of the insulating layer 44), the formation of a second thermoplastic layer 48 on the previously formed first thermoplastic layer 20, on the first thermal via 30 and on the electrical connection structure 40. The formation of the second thermoplastic layer 48 is similar to the formation previously described with reference to Figure 6A , and therefore it is not described in detail again.

[0080] After the formation of the second thermoplastic layer 48, the steps similar to those described with reference to Figure 6B -6D are then carried out (and therefore not described again) to form a second thermal via 50 on the first thermal via 30 so that the second thermal via 50 is vertically superimposed on the first thermal via 30 and is in direct physical contact with the first thermal via 30 to form a thermal via 54 with the first thermal via 30, the thermal via 54 traversing the thermoplastic layer 52 from the top surface 52a up to the top electrically insulating layer 130 of the thermoelectric cell 100.

[0081] Figure 8 An embodiment of the generator 10 is shown in which the generator 10 comprises a plurality of thermoelectric cells 100 arranged in a matrix parallel to the XY plane. Each thermoelectric cell 100 is connected to a respective first thermal via 30 (or similarly, to a respective thermal via 54), visible in Figure 1 on the top surface 20a in a respective matrix arrangement (for simplicity of display, Figure 8 the thermal coupling layer 32 is not shown). As previously described, each thermoelectric cell 100 comprises a respective cavity 115, Figure 8not shown, as it is inside the generator 10, is not visible in the perspective view of Figure 8

[0082] Figure 9 Another embodiment of the generator 10 is shown. By way of example, Figure 9 The generator 10 of the embodiment of Figure 7 ; however, it is clear that the following considerations apply equally to other embodiments of the generator 10.

[0083] In particular, Figure 9 The generator 10 of the embodiment has leads 45 extending on one (or respective) PCBs (“Printed Circuit Boards”) 64, which in turn extend on the heat sink 14. In addition, optionally, a thermally conductive intermediate element 66 (also known as “thermal socket”) is present between the heat sink 14 and the die pad 16 (for example, fixed to the die pad 16 by means of an electrically insulating layer 60) to allow the die pad 16 to exchange heat with the heat sink 14. In detail, the thermally conductive intermediate element 66 is made of a thermally conductive material such as metal (for example, aluminum) and has a thickness along the Z axis substantially equal to the thickness of the PCBs 64 and, in any case, such that it allows the die pad 16 to exchange heat with the heat sink 14.

[0084] Figure 12 An application example of the generator 10 is shown. In particular, Figure 12 A heating system 500 comprising a heating device 502 (for example, a radiator such as a domestic radiator) and a control device 504 is shown. The heating device 502 comprises a thermal valve 508 that regulates the level of heat produced by the heating device 502, for example, in a manner known per se. The control device 504 is connected to the heating device 502 to receive heat from the heating device 502 and, for example, to control its operation (in detail, to control the thermal valve 508 and thus to regulate the level of heat produced by the heating device 502). The control device 504 comprises the generator 10 and a control unit 506 (for example, a CPU or a dedicated microprocessor) that are electrically coupled to each other, for example. In particular, the generator 10 is coupled to the heating device 502 to receive heat from the heating device 502 (which operates as a heat source 12) and, for example, to generate electrical power that powers the control unit 506, which in turn is coupled to the thermal valve 508 to control its operation. Optionally, the control device 504 can further comprise a unit configured to be recharged by the power supply provided by the generator 10 and to power the control unit 506 and the thermal valve 508. In this way, the thermal valve 508 is controlled by the control device 504, which is autonomously powered by the heat produced by the heating device 502, thus not requiring to be connected to an external power supply.

[0085] The advantages offered by the present disclosure are evident from the examination of the features thereof.

[0086] ​In detail, the generator 10 is an integrated device that allows the conversion from thermal energy to electrical energy. The generator 10 can be made using low-cost and simple MEMS technology, using materials with reduced environmental impact and easily found.

[0087] Moreover, as an integrated device, the generator 10 occupies a small volume and can generate electrical power of the order of mW, and therefore it can be used in applications such as the driving of thermal valves, such as radiators.

[0088] The generator 10 allows the passage of the thermal flow through the thermoelectric microstructures 110N and 110P (with reduced thickness, for example equal to a few thousand Angstroms, for example up to 1-2 pm), which are of the planar type and therefore provide a substantially planar (horizontal) thermoelectric power generation structure. This makes the generator 10 more competitive from an industrial point of view (with reduced production costs), simpler and more mechanically stable from a manufacturing point of view.

[0089] Moreover, thanks to the thermal vias 30, 54 (thermally conductive, for example with a thermal conductivity equal to a few hundred W m －1 K －1 , for example about 400 W m －1 K －1 ) immersed in the thermoplastic layers 20, 52 (thermally insulating, for example with a thermal conductivity lower than a few W m －1 K －1 , for example about 0.8 W m －1 K －1 , these high temperature gradients (for example, a temperature difference of a few tens of °C through the thermoelectric microstructures 110N and 110P) can be obtained in a planar structure, said thermal vias 30, 54 having a thickness of suitable dimensions along the Z axis to prevent the exchange of heat between the heat source 12 and the thermoelectric cell 100, thus ensuring the desired temperature gradient (for example, a thickness equal to a few pm or tens of pm) through the thermoelectric microstructures 110N and 110P. For example, about 10 pm).

[0090] Finally, it is clear that modifications and / or additions of, for details, can be made to the disclosure described and illustrated herein, without departing from the scope of the present disclosure. For example, the different embodiments described can be combined with each other to provide further solutions.

[0091] Moreover, the thermoelectric cell 100 can comprise only one thermoelectric element 110.

[0092] Moreover, as Figure 10As shown in the embodiment of the generator 10, each electrical connection structure 40 may include a conductor 66 of a corresponding conductive material (e.g., a metal such as gold or copper) and has a first end 66a and a second end 66b opposite to each other along the main extension direction of the conductor 66. In each conductor 66, the first end 66a is coupled to a corresponding conductive terminal 132 and the second end 66b is coupled to a corresponding lead 45, such that it electrically connects the conductive terminal 132 to the corresponding lead 45.

[0093] Figure 11A - Figure 11B It shows Figure 10 The various steps in the manufacturing process of the generator 10.

[0094] First, a reference will be provided, which will not be discussed further. Figure 5A - Figure 5H The thermoelectric unit 100.

[0095] Subsequently, reference Figure 11A The thermoelectric unit 100 is fixed to the die pad 16 by the adhesive layer 18. Furthermore, the die pad 16 and lead 45 are fixed to the heat sink 14, for example, by known die attachment techniques. Additionally, the wire 66 is fixed to the corresponding conductive terminal 132 and the corresponding lead 45 by wire bonding techniques known per se.

[0096] Subsequently, reference Figure 11B A first thermoplastic layer 20 is formed on the thermoelectric unit 100 and the lead wire 45, such that it surrounds the conductor 66 to thermally insulate them from the external environment. The first thermoplastic layer 20 is constructed as previously described... Figure 6A The aforementioned injection molding.

[0097] Then, similar to Figure 6B - Figure 6D The manufacturing steps described herein then involve forming a first thermal via 30 through the first thermoplastic layer 20, at its end obtaining... Figure 10 The generator.

[0098] The thermoelectric unit 100 may further include thermoelectric elements 110 that are vertically overlapping each other along the Z-axis. Specifically, as shown in the figure... Figure 13 and Figure 14 As shown, the serpentine arrangement of thermoelectric microstructures 110N and 110P can be repeated along the Z-axis on more layers (i.e., at different heights relative to the substrate 105). This allows for an increase in the total potential difference between the conductive terminals 132, where the surfaces of the heat source 12 and the thermoelectric units receive the same amount of heat in the XY plane.

[0099] As an example, Figure 13 and Figure 14Thermoelectric unit 100 with two stacked levels of thermoelectric microstructures 110N and 110P is shown; however, similar considerations apply to cases where there are more than two stacked layers of thermoelectric microstructures 110N and 110P. In detail, Figure 13 Along Figure 14 The section cut by the cross-section XII-XII shows a portion of the thermoelectric unit 10, which corresponds to the portion including a first portion 105L of the substrate 105 and a portion of the cavity 115 (in other words, only the left half of the thermoelectric unit 100 is shown, while the right half including the second portion 105R of the substrate 105 is not shown for simplicity). On the other hand, Figure 14 yes Figure 13 A top view of the thermoelectric unit 100 parallel to the XY plane.

[0100] like Figure 14 As shown, the thermoelectric unit 100 may include a first thermoelectric microstructure 110N′, 110P′ extending with a first height relative to a substrate 105 (e.g., measured along the Z-axis relative to a first surface 105a of the substrate 105) and a second thermoelectric microstructure 110N″, 110P″ extending with a second height relative to the substrate 105 (e.g., also measured along the Z-axis relative to the first surface 105a of the substrate 105), wherein the second height is lower than the first height. As an example, Figure 13 A first P-type thermoelectric microstructure 110P′ and a second N-type thermoelectric microstructure 110N″ are shown. Specifically, the second N-type thermoelectric microstructure 110N″ extends into the bottom electrical insulating layer 120, while the first P-type thermoelectric microstructure 110P′ extends on the bottom electrical insulating layer 120 such that it is vertically superimposed on the second N-type thermoelectric microstructure 110N″. The conductive elements 125 of the second thermoelectric microstructures 110N″, 110P″ extend from the respective second thermoelectric microstructures 110N″, 110P″ until they protrude beyond the bottom electrical insulating layer 120, thereby allowing electrical connection of the second thermoelectric microstructures 110N″, 110P″.

[0101] like Figure 14 As shown, the first thermoelectric microstructures 110N′ and 110P′ are connected to each other via conductive element 125 and have similar properties to a reference. Figure 2 The first serpentine arrangement discussed; in addition, the second thermoelectric microstructures 110N″, 110P″ (in Figure 14 (Seen in dashed lines because they are placed at different heights relative to the first thermoelectric microstructures 110N′, 110P′) they are connected to each other via corresponding conductive elements 125 and have a reference-like structure between them. Figure 2The second serpentine arrangement is discussed. The electrically conductive terminals 132 are provided at the ends of the two serpentine arrangements. In other words, the first thermoelectric microstructures 110N', 110P' and the second thermoelectric microstructures 110N", 110P" are electrically arranged in parallel to each other.

[0102] Alternatively, and in a manner not shown, the first thermoelectric microstructures 110N', 110P' and the second thermoelectric microstructures 110N", 110P" are placed electrically in series to each other. This is achieved for each pair of thermoelectric microstructures superimposed to each other by electrically contacting, through an electrically conductive element 125, one end of the first thermoelectric microstructure 110N', 110P' with the corresponding end of the second thermoelectric microstructure 110P", 110N" having opposite electrical conductivity (e.g. the first end 110' of the first P-type thermoelectric microstructure 110P' with the first end 110' of the second N-type thermoelectric microstructure 110N") and by electrically contacting, through another electrically conductive element 125, the other end of the first thermoelectric microstructure 110N', 110P' with the corresponding other end of the second thermoelectric microstructure 110P", 110N" having opposite electrical conductivity, said pair of thermoelectric microstructures being in serpentine arrangement with the considered pair (e.g. the second end 110" of the first P-type thermoelectric microstructure 110P' with the second end 110" of the second N-type thermoelectric microstructure 110N" of the contiguous pair).

[0103] Figure 13 and 14 The thermoelectric unit 100 of Figure 5A - Figure 5D is provided in the following manner. First, the manufacturing steps described with reference to Figure 5B -5D are performed to form the second thermoelectric microstructures 110N", 110P". Subsequently, another layer of insulating material, e.g. oxide (e.g. silicon oxide), is formed on the bottom electrically insulating layer 120 and on the second thermoelectric microstructures 110N", 110P" to increase the thickness of the bottom electrically insulating layer 120 and, subsequently, another layer of thermoelectric material 204 is formed on the increased type of bottom electrically insulating layer 120. Thereafter, the steps of Figure 5E -5D are repeated to form the first thermoelectric microstructures 110N', 110P' on the increased type of bottom electrically insulating layer 120. Finally, the steps of Figure 14 -5H are performed to obtain the thermoelectric unit 100 of Figure 5F ( in detail, the electrically conductive elements 125 of the first thermoelectric microstructures 110N', 110P' and of the second thermoelectric microstructures 110N", 110P" are provided in the step of

[0104] A MEMS thermoelectric generator (10) can be summarized as comprising at least one thermoelectric cell (100) including a substrate (105) of semiconducting material having a first surface (105a) and a second surface (105b) opposite each other along a first axis (Z), wherein a cavity (115) extends into the substrate (105) from the second surface (105b) along the first axis (Z) up to the first surface (105a); an electrically insulating layer (120, 130) of electrically insulating material extending over the first surface (105a) of the substrate (105) and over the cavity (115); one or more thermoelectric elements (110) of thermoelectric material, each thermoelectric element (110) extending into the electrically insulating layer (120, 130) having a first end (110') and a second end (110") opposite each other along a second axis (X) orthogonal to the first axis (Z) and configured to convert a thermal drop between the first end (110') and the second end (110") into an electric potential between the first end (110') and the second end (110") by the Seebeck effect, wherein the first end (110') of each thermoelectric element (110) is superimposed on the cavity (115) along the first axis (Z) and the second end (110") of each thermoelectric element (110) is superimposed on the substrate (105) along the first axis (Z), the MEMS thermoelectric generator (10) further comprising a thermoplastic layer (20; 20, 48) extending over the electrically insulating layer (120, 130) and having a top surface (20a; 52a) and a bottom surface (20b) opposite each other along the first axis (Z), the bottom surface (20b) of the thermoplastic layer (20; 20, 48) facing the electrically insulating layer (120, 130), the thermoplastic layer (20; 20, 48) being made of thermally insulating material and configured to be processed by a Laser Direct Structuring, LDS, technique; a heat sink (14) coupled to the thermoelectric cell and configured to exchange heat with the thermoelectric cell (100), the thermoelectric cell (100) extending along the first axis (Z) between the heat sink (14) and the thermoplastic layer (20); and a via (30; 30, 50) of thermally metallic material extending through the thermoplastic layer (20; 20, 48) from the top surface (20a; 52a) to the bottom surface (20b) of the thermoplastic layer (20); the MEMS thermoelectric generator (10) being capable of having a heat source (12) to generate a thermal drop between the first end (110') and the second end (110") of each thermoelectric element (110) with the top surface (20a; 52a) of the thermoplastic layer (20; 20, 48) facing the heat source (12) and the thermoelectric cell (100) exchanging heat through the thermal via (30; 30, 50).

[0105] The thermoplastic layer (20; 20, 48) can be a thermoplastic polymeric material doped with an organometallic compound configured to be chemically activated when irradiated by a laser beam.

[0106] The thermoelectric unit (100) can comprise a first plurality of the thermoelectric elements (110), wherein the first plurality of thermoelectric elements (110) can comprise a respective first plurality of thermoelectric microstructures (110N', 110P') interconnected by electrically conductive elements (125) to form a first serpentine arrangement, wherein the first plurality of thermoelectric microstructures (110N', 110P') can comprise thermoelectric microstructures (110N'; 110P') having a first conductivity type and thermoelectric microstructures (110N'; 110P') having a second conductivity type opposite to the first conductivity type; wherein the thermoelectric elements (110) and the electrically conductive elements (125) are embedded in the electrically insulating layer (120, 130).

[0107] The thermoelectric unit (100) can further comprise a second plurality of the thermoelectric elements (110), wherein the second plurality of thermoelectric elements (110) can comprise a respective second plurality of thermoelectric microstructures (110N", 110P") interconnected by respective electrically conductive elements (125) to form a second serpentine arrangement, wherein the second plurality of thermoelectric microstructures (110N", 110P") can comprise respective thermoelectric microstructures (110P"; 110N") having a first conductivity type and thermoelectric microstructures (110N"; 110P") having a second conductivity type opposite to the first conductivity type; wherein the first plurality of thermoelectric microstructures (110N', 110P') can be superimposed on the second plurality of thermoelectric microstructures (110N", 110P") along the first axis (Z), and wherein the first and second pluralities of thermoelectric microstructures (110N', 110P') can be electrically arranged with respect to each other in series, in a first and second serpentine arrangement coinciding; or in parallel.

[0108] The thermoelectric unit (100) can further comprise electrically conductive terminals (132) arranged at the ends of the first serpentine arrangement and in electrical contact with the thermoelectric elements (110), for each electrically conductive terminal (132) the MEMS thermoelectric generator can further comprise a respective lead (45) extending on the heat sink (14) transversely to the thermoelectric unit (100) so that it is electrically insulated with respect to the heat sink (14) or on a PCB (64) fixed to the heat sink (14) from the thermoplastic layer (20; 20, 48) and it also extends on the lead (45); and for each electrically conductive terminal (132) a respective electric connection structure (40) of a metallic material extending at least partially into the thermoplastic layer (20; 20, 48) and electrically coupling the respective electrically conductive terminal (132) with the respective lead (45).

[0109] The thermoplastic layer (20) can be formed by a first thermoplastic layer (20) having the top surface (20a) and the bottom surface (20b), wherein the thermal via (30) can be formed by a first thermal via (30) having a first end (30') and a second end (30") opposite each other along the first axis (Z), the first end (30') of the first thermal via (30) facing the top surface (20a) of the thermoplastic layer (20) and the second end (30") of the first thermal via (30) being in contact with the electrically insulating layer (120, 130) so that it can be superimposed on the first end (110') of each thermoelectric element (110) along the first axis (Z), wherein each electric connection structure (40) can comprise a first electric via (41), a second electric via (42) and an electric connection portion (43) connecting the first electric via (41) and the second electric via (42), wherein the first electric via (41) can extend transversely to the first thermal via (30) from the top surface (20a) of the thermoplastic layer (20) through the first thermoplastic layer (20) to the thermoelectric unit (100) so that it is in electrical contact with the respective electrically conductive terminal (132), wherein the second electric via (42) can extend transversely to the first electric via (41) through the first thermoplastic layer (20) from the first thermoplastic layer (20) of the thermoplastic layer (20) to the respective lead (45) so that the first thermoplastic layer (20) is in electrical contact with the respective lead (45), wherein the electric connection portion (43) can extend on the top surface (20a) of the thermoplastic layer (20) between the first electric via (41) and the second electric via (42) so that the first electric via (41) and the second electric via (42) are in electrical contact with each other, and wherein an insulating layer (44) of an insulating material can extend on the electric connection portion (43).

[0110] The thermoplastic layer (20, 48) can be formed by a first thermoplastic layer (20) and a second thermoplastic layer (48) extending on and integral with the first thermoplastic layer (20), the first thermoplastic layer (20) defining the bottom surface (20b) of the thermoplastic layer (20, 48) and the second thermoplastic layer (48) defining the top surface (52a), and wherein the thermal via (30, 50) can be formed by a first thermal via (30) and a second thermal via (50) extending on and integral with the first thermal via (30), the first thermal via (30) extending through the first thermoplastic layer (20) and the second thermal via (50) extending through the second thermoplastic layer (48), the thermal via (30, 50) having a first end (50') and a second end (30") opposite each other along the first axis (Z), the first end (50') of the thermal via (30, 50) being part of the second thermal via (50) and facing the top surface (52a) of the thermoplastic layer (20, 48), the second end (30") of the thermal via (30, 50) being part of the first thermal via (30) and being in contact with the electrically insulating layer (120, 130), so that the second end (30") of the thermal via (30, 50) is superimposed on the first end (110') of each thermoelectric element (110) along the first axis (Z), wherein each electrical connection structure (40) can comprise a first electrical via (41), a second electrical via (42) and an electrical connection via (43), the electrical connection via (43) being interposed between the first thermoplastic layer (20) and the second thermoplastic layer (48) along the first axis (Z) and connecting the first electrical via (41) and the second electrical via (42), wherein the first electrical via (41) can extend laterally from the electrical connection portion (43) to the first thermal via (30) through the first thermoplastic layer (20), so as to be in electrical contact with the corresponding electrically conductive terminal (132), wherein the second electrical via (42) can extend laterally to the first electrical via (41) from the electrical connection portion (43) to the corresponding lead (45) through the first thermoplastic layer (20), so as to be in electrical contact with the corresponding lead (45), and wherein the electrical connection portion (43) can extend between the first electrical via (41) and the second electrical via (42) along the second axis (X), so as to be in electrical contact with each other.

[0111] Each electrical connection structure (40) can include a respective metallic material wire (66) extending into the thermoplastic layer (20) and having first and second ends (66a, 66b) opposite each other, the first end (66a) of the wire (66) being secured to the respective electrically conductive terminal (132), the second end (66b) of the wire (66) being secured to the respective lead (45).

[0112] The one or more thermoelectric elements (110) can be polycrystalline silicon or polycrystalline silicon-germanium.

[0113] A manufacturing process of a MEMS thermoelectric generator (10), which can be summarized as comprising the steps of: forming an electrically insulating layer (120, 130) of electrically insulating material on a first surface (105a) of a substrate (105) of semiconductor material, said substrate (105) further having a second surface (105b) opposite said first surface (105a) along a first axis (Z), wherein one or more thermoelectric elements (110) of thermoelectric material extend into said electrically insulating layer (120, 130), each thermoelectric element (110) having a first end (110') and a second end (110") opposite each other along a second axis (X) orthogonal to the first axis (Z) and being configured to convert a thermal drop between the first end (110') and the second end (110") into an electric potential between the first end (110') and the second end (110") by the Seebeck effect; and forming a cavity (115) in said substrate (105) extending from said second surface (105b) of said substrate (105) to said first surface (105a) of said substrate (105), wherein said first end (110') of each thermoelectric element (110) is superimposed on said cavity (115) along said first axis (Z) and said second end (110") of each thermoelectric element (110) is superimposed on said substrate (105) along said first axis (Z), and wherein said substrate (105), said electrically insulating layer (120, 130) and said one or more thermoelectric elements (110) define a thermoelectric cell (100) of said MEMS thermoelectric generator (10), said manufacturing process further comprising the steps of: coupling said thermoelectric cell (100) to a heat sink (14) configured to exchange heat with said thermoelectric cell (100), said heat sink (14) facing said second surface (105b) of said substrate (105); forming a thermoplastic layer (20; 20, 48) on said electrically insulating layer (120, 130), the thermoplastic layer (20; 20, 48) having a top surface (20a; 52a) and a bottom surface (20b) opposite each other along the first axis (Z), the bottom surface (20b) of the thermoplastic layer (20; 20, 48) facing the electrically insulating layer (120, 130), the thermoplastic layer (20; 20, 48) being made of thermally insulating material and being configured to be processed by a laser direct structuring, LDS, technique; and forming a thermal via (30; 30, 50) of metallic material in said thermoplastic layer (20; 20, 48) extending from said top surface (20a; 52a) to said bottom surface (20b) of said thermoplastic layer (20); said MEMS thermoelectric generator (10) being capable of being used in such a way that said top surface (20a; 52a) of the thermoplastic layer (20; 20, 48) faces said heat source (12) and said thermoelectric cell (100) exchanges heat through said thermal via (30).It has a heat source (12) to generate a thermal drop between a first end (110') and a second end (110") of each thermoelectric element (110).

[0114] The step of forming the electrically insulating layers (120, 130) can comprise: a. forming a bottom electrically insulating layer (120) of electrically insulating material on the first surface (105a) of the substrate (105); b. forming a thermoelectric material layer (204) of thermoelectric material on the bottom electrically insulating layer (120); c. forming at least one first doped portion (206N) in the thermoelectric material layer (204) by doping at least one respective first exposed region (204N) of the thermoelectric material layer (204) with a dopant having a first conductivity type; d. removing the thermoelectric material layer (204) leaving the at least one first doped portion (206N) on the bottom electrically insulating layer (120), each first doped portion (206N) forming a respective thermoelectric element (110N) having the first conductivity type of the thermoelectric elements (110); e. forming a first insulating layer (129) of electrically insulating material on the bottom electrically insulating layer (120) and each thermoelectric element (110), the first insulating layer (129) comprising a top electrically insulating layer (130), the bottom electrically insulating layer (120) and the top electrically insulating layer (130) defining the electrically insulating layers (120, 130).

[0115] The step of forming the electrically insulating layers (120, 130) can further comprise, between steps c and d: forming at least one second doped portion (206P) laterally from the at least one first exposed region (204N) in the thermoelectric material layer (204) by doping at least one second exposed region (204P) of the thermoelectric material layer (204) with a further dopant having a second conductivity type opposite to the first type; during step d., removing the thermoelectric material layer (204) leaving the at least one first doped portion (206N) and the at least one second doped portion (206P) on the bottom electrically insulating layer (120), each second doped portion (206P) forming a respective thermoelectric element (110P) having the second conductivity type of the thermoelectric elements (110); after step e., forming at least one electrically conductive element (125) of electrically conductive material through the first insulating layer (129), the electrically conductive element (125) of electrically conductive material electrically contacting respective thermoelectric elements (110N) having the first conductivity type and respective thermoelectric elements (110P) having the second conductivity type to interconnect them; and forming one or more second insulating layers of electrically insulating material on the first insulating layer (129) and the at least one electrically conductive element (125), the second insulating layers defining the top electrically insulating layer (130) together with the first insulating layer (129).

[0116] The step of forming the cavity (115) in the substrate (105) can comprise temporarily coupling the thermoelectric unit (100) to a transport wafer (216) facing the electrically insulating layer (120, 130) of the thermoelectric unit (100); etching at a cavity region (220) of the second surface (105b) of the substrate (105) to form the cavity (115), the cavity region (220) being aligned along the first axis (Z) with the first end (110') of each thermoelectric element (110); and decoupling the thermoelectric unit (100) and the transport wafer (216) from each other.

[0117] The step of forming the thermoplastic layer (20; 20, 48) can comprise forming a first thermoplastic layer (20) on the electrically insulating layer (120, 130) by injection molding, the first thermoplastic layer (20) being the thermoplastic layer (20) or being a part of the thermoplastic layer (20, 48).

[0118] The step of forming the thermal via (30; 30, 50) in the thermoplastic layer (20; 20, 48) can comprise forming a first trench (140) in the first thermoplastic layer (20) from a top surface (20a) to a bottom surface (20b) of the first thermoplastic layer (20), the first trench (140) being formed by selectively removing corresponding portions of the first thermoplastic layer (20) by laser radiation of a first trench region of the top surface (20a) of the first thermoplastic layer (20) by means of a LDS technique, the first trench region being superimposed on the cavity (115) along the first axis (Z); and performing a metal deposition in the first trench (140) to form a first thermal via (30), the first thermal via (30) being the thermal via (30) or being a part of the thermal via (30, 50).

[0119] The thermoelectric unit (100) can comprise a plurality of said thermoelectric elements (110) interconnected to form a serpentine arrangement, the manufacturing process can further comprise the steps of: forming conductive terminals (132) in the electrically insulating layer (120, 130), the conductive terminals (132) being placed at the extremities of the serpentine arrangement and being exposed by the electrically insulating layer (120, 130); for each conductive terminal (132), forming in the first thermoplastic layer (20) from the top surface (20a) of the first thermoplastic layer (20) up to the bottom surface (20b) a corresponding second trench (141) and a corresponding third trench (142), the corresponding second and third trenches (141, 142) being laterally arranged to the first trench (140) and being formed by selectively removing corresponding portions of the first thermoplastic layer (20) by laser irradiation of corresponding second and third trench areas of the top surface (20a) of the first thermoplastic layer (20) by means of the LDS technique, the corresponding second and third trench areas being respectively superimposed on the corresponding conductive terminal (132) along the first axis (Z) and laterally extending on the heat spreader (14) onto a respective lead (45) of the thermoelectric unit (100), the first thermoplastic layer (20) being also formed on the respective lead (45); for each conductive terminal (132), chemically activating a corresponding activation area (143) of the top surface (20a) of the first thermoplastic layer (20) by laser irradiation using the LDS technique, the activation area extending between the corresponding second and third trench areas; and performing metal deposition in the second and third trenches (141, 142) to form a respective first electrical via (41) and a second electrical via (42), and performing metal deposition on the activation area (143) to form a respective electrical connection portion (43) interposed between the respective first and second electrical vias (41, 42) along the second axis (X), the respective first and second electrical vias (41, 42) and the respective electrical connection portion (43) together forming a respective electrical connection structure (40) electrically connecting the respective conductive terminal (132) and the respective lead (45) to each other.

[0120] The manufacturing process can further comprise a step of forming an insulating layer (44) of insulating material on each of the electrical connection structures (40), or can further comprise a step of forming a second thermoplastic layer (48) on the first thermoplastic layer (20), on the electrical connection structures (40) and on the first thermal via (30) by injection molding, the second thermoplastic layer (48) forming, together with the first thermoplastic layer (20), said thermoplastic layer (20, 48); and forming a second thermal via (50) of metallic material in said second thermoplastic layer (48), said second thermal via (50) overlapping said first thermal via (30) along said first axis (Z), said first thermal via (30) and said second thermal via (50) forming said thermal via (30, 50).

[0121] Said thermoelectric unit (100) can comprise a plurality of said thermoelectric elements (110) interconnected to form a serpentine arrangement, said manufacturing process can further comprise, before forming said thermoplastic layer (20) on said electrically insulating layer (120, 130), the steps of: forming electrically conductive terminals (132) in said electrically insulating layer (120, 130), said electrically conductive terminals (132) being placed at the ends of said serpentine arrangement and being exposed by said electrically insulating layer (120, 130); fixing a first end (66a) of a respective wire (66) to each electrically conductive terminal (132) and fixing a second end (66b) of said respective wire (66) to a respective lead (45), the first end (66a) and the second end (66b) of each wire (66) being opposite each other, each lead (45) extending transversely to the thermoelectric unit (100) on a heat sink (14); and forming said thermoplastic layer (20) also on said wires (66).

[0122] A heating system (500) is outlined comprising a heating device (502) and a control device (504), said control device (504) comprising a MEMS thermoelectric generator (10) according to any one of claims 1-9, said MEMS thermoelectric generator (10) being coupled to said heating device (502) to exchange heat with said heating device (502), said heating device (502) being said heat source (12).

[0123] The various embodiments described above can be combined to provide further embodiments. If desired, aspects of different embodiments can be modified and / or combined to provide additional embodiments.

[0124] These and other changes can be made to the embodiments in light of the above Detailed Description. The terms used in the following claims should not be construed to limit the claims present application to the specific embodiments disclosed in the specification and the claims. The scope of the application is to be interpreted only from the claims.

Claims

1. A microelectromechanical system (MEMS) thermoelectric generator comprising: at least one thermoelectric cell comprising: a substrate of semiconductor material having a cavity between a first surface of the substrate and a second surface of the substrate opposite each other along a first direction; an electrically insulating layer on the first surface of the substrate and over the cavity; and one or more thermoelectric elements in the electrically insulating layer, each of the one or more thermoelectric elements having a first end and a second end opposite each other along a second direction transverse to the first direction, and each thermoelectric element being configured to convert a thermal drop between the first end and the second end into an electrical potential between the first end and the second end by the Seebeck effect, the first end of each thermoelectric element being over the cavity and the second end of each thermoelectric element being over the substrate; a thermoplastic layer extending over the at least one thermoelectric cell, the thermoplastic layer being made of a thermally insulating material and being configured to be processed by a laser direct structuring (LDS) technique; a heat sink coupled to the first end of the at least one thermoelectric cell and configured to exchange heat with the thermoelectric cell, the heat sink being opposite a first surface of the thermoplastic layer; and a thermal via of a metallic material extending from the electrically insulating layer through the thermoplastic layer to the first surface of the thermoplastic layer, the thermal via being over the first end of each thermoelectric element; wherein the MEMS thermoelectric generator is coupleable to a heat source, wherein the first surface of the thermoplastic layer faces the heat source, and the at least one thermoelectric cell exchanges heat with the heat source through the thermal via to generate the thermal drop between the first end and the second end of each thermoelectric element.

2. The MEMS thermoelectric generator of claim 1, wherein the at least one thermoelectric cell comprises a first plurality of the thermoelectric elements; wherein the first plurality of thermoelectric elements comprises a respective first plurality of thermoelectric microstructures, the first plurality of thermoelectric microstructures being interconnected by electrically conductive elements to form a first serpentine arrangement, wherein the first plurality of thermoelectric microstructures comprises first thermoelectric microstructures having a first conductivity type and second thermoelectric microstructures having a second conductivity type different from the first conductivity type, the first thermoelectric microstructures having the first conductivity type and the second thermoelectric microstructures having the second conductivity type being alternated with each other along the first serpentine arrangement, and wherein the thermoelectric elements and the electrically conductive elements are buried in the electrically insulating layer.

3. The MEMS thermoelectric generator of claim 2, wherein the thermoelectric cell comprises a second plurality of the thermoelectric elements; wherein the second plurality of thermoelectric elements comprises a respective second plurality of thermoelectric microstructures, the second plurality of thermoelectric microstructures being interconnected by respective electrically conductive elements to form a second serpentine arrangement, wherein the second plurality of thermoelectric microstructures includes respective first thermoelectric microstructures having the first conductivity type and respective second thermoelectric microstructures having the second conductivity type, the first and second thermoelectric microstructures alternating with each other along the second serpentine arrangement, wherein the first plurality of thermoelectric microstructures is superimposed on the second plurality of thermoelectric microstructures along the first direction, and wherein the first and second plurality of thermoelectric microstructures are arranged in electrical series with each other, the first and second serpentine arrangements being coincident or in parallel.

4. The MEMS thermoelectric generator of claim 2, wherein the thermoelectric unit includes electrically conductive terminals disposed at ends of the first serpentine arrangement, the electrically conductive terminals being in electrical contact with the thermoelectric elements, each electrically conductive terminal being electrically coupled to a respective lead via a respective electrical connection structure, the leads being electrically insulated from the heat spreader, the thermoplastic layer extending over the leads, and the electrical connection structure of the respective metallic material extending at least partially into the thermoplastic layer.

5. The MEMS thermoelectric generator of claim 4, wherein the thermoplastic layer includes a first thermoplastic layer having the first surface; wherein the thermal via includes a first thermal via having first and second ends opposite each other along the first direction, the first end of the first thermal via facing the first surface of the thermoplastic layer, and the second end of the first thermal via being in contact with the electrically insulating layer such that the second end of the first thermal via is superimposed on the first end of each thermoelectric element along the first direction; wherein each electrical connection structure includes a first electrical via, a second electrical via, and an electrical connection portion connecting the first and second electrical vias; wherein the first electrical via extends from the first surface of the thermoplastic layer through the first thermoplastic layer to the thermoelectric unit such that the first electrical via is in electrical contact with the respective electrically conductive terminal; wherein the second electrical via extends from the first surface of the thermoplastic layer through the first thermoplastic layer to the respective lead such that the second electrical via is in electrical contact with the respective lead; wherein the electrical connection portion extends on the first surface of the thermoplastic layer between the first and second electrical vias such that the first and second electrical vias are in electrical contact with each other; and wherein an insulating layer of insulating material extends over the electrical connection portion.

6. The MEMS thermoelectric generator of claim 4, wherein the thermoplastic layer includes a first thermoplastic layer and a second thermoplastic layer, the second thermoplastic layer extending over and being integral with the first thermoplastic layer, the second thermoplastic layer defining the first surface of the thermoplastic layer, and wherein the thermal via includes a first thermal via and a second thermal via extending over and integral with the first thermal via, the first thermal via extending through the first thermoplastic layer, the second thermal via extending through the second thermoplastic layer, the thermal via having first and second ends opposite each other along the first direction, the first end of the thermal via being part of the second thermal via and facing the first surface of the thermoplastic layer, the second end of the thermal via being part of the first thermal via and in contact with the electrically insulating layer, such that the second end of the thermal via overlaps the first end of each thermoelectric element along the first direction; wherein each electrical connection structure includes a first electrical via, a second electrical via, and an electrical connection via interposed between the first and second thermoplastic layers along the first direction and connecting the first and second electrical vias; wherein the first electrical via extends from the electrical connection portion through the first thermoplastic layer to the thermoelectric unit, such that the first electrical via is in electrical contact with the respective electrically conductive terminal; wherein the second electrical via extends from the electrical connection portion through the first thermoplastic layer to the respective lead, such that the second electrical via is in electrical contact with the respective lead; and wherein the electrical connection portion extends between the first and second electrical vias along the second direction, such that the first and second electrical vias are in electrical contact with each other.

7. The MEMS thermoelectric generator of claim 4, wherein each electrical connection structure includes a respective metallic material wire extending into the thermoplastic layer and having first and second ends opposite each other, the first end of the wire being secured to the respective electrically conductive terminal, the second end of the wire being secured to the respective lead.

8. A method of manufacturing a MEMS thermoelectric generator, the method comprising: forming an electrically insulating layer of electrically insulating material on a first surface of a substrate of semiconductor material, the substrate having a second surface opposite the first surface along a first direction, one or more thermoelectric elements of thermoelectric material formed in the electrically insulating layer, each thermoelectric element having first and second ends opposite each other along a second direction transverse to the first direction, and each thermoelectric element configured to convert a thermal drop between the first and second ends into an electrical potential between the first and second ends by the Seebeck effect; forming a cavity in the substrate extending from the second surface of the substrate to the first surface of the substrate, the first end of each thermoelectric element being superimposed on the cavity along the first direction, and the second end of each thermoelectric element being superimposed on the substrate along the first direction; wherein the substrate, the electrically insulating layer, and the one or more thermoelectric elements define a thermoelectric unit of the MEMS thermoelectric generator; coupling the thermoelectric unit to a heat sink configured to exchange heat with the thermoelectric unit, the heat sink facing the second surface of the substrate; forming a first thermoplastic layer on the electrically insulating layer, the first thermoplastic layer having a first surface and a second surface opposite each other along the first direction, the second surface of the electrically insulating layer facing the electrically insulating layer, the first thermoplastic layer being made of a thermally insulating material and configured to be processed by a laser direct structuring, LDS, technique; and forming a first thermal via of a metallic material in the first thermoplastic layer, the first thermal via extending from the first surface to the second surface of the first thermoplastic layer, such that the first thermal via is superimposed on the first end of each thermoelectric element along the first direction; wherein the MEMS thermoelectric generator is capable of being coupled to a heat source such that the first surface of the first thermoplastic layer faces the heat source, and the thermoelectric unit exchanges heat with the heat source through the first thermal via to generate the thermal drop between the first end and the second end of each thermoelectric element.

9. The manufacturing method of claim 8, wherein forming the electrically insulating layer comprises: forming a second electrically insulating layer of an electrically insulating material on the first surface of the substrate; forming a thermoelectric material layer of a thermoelectric material on the second electrically insulating layer; forming at least one first doped portion in the thermoelectric material layer by doping at least one respective first exposed region of the thermoelectric material layer with a doping substance having a first conductivity type; removing the thermoelectric material layer, thereby leaving the at least one first doped portion on the second electrically insulating layer, each first doped portion forming a respective thermoelectric element having the first conductivity type of the thermoelectric element; and forming a first insulating layer comprising the electrically insulating material in a first electrically insulating layer on the second electrically insulating layer and on each thermoelectric element, the second electrically insulating layer and the first electrically insulating layer defining the electrically insulating layer.

10. The manufacturing method of claim 9, wherein forming the electrically insulating layer comprises: forming at least one second doped portion in the thermoelectric material layer by doping at least one second exposed region of the thermoelectric material layer spaced apart from the at least one first exposed region with a further doping substance having a second conductivity type opposite the first conductivity type, after forming the at least one first doped portion and before removing the thermoelectric material layer; wherein removing the thermoelectric material layer comprises leaving both the at least one first doped portion and the at least one second doped portion on the second electrically insulating layer, each second doped portion forming a respective thermoelectric element having the second conductivity type of the thermoelectric element; after forming the first insulating layer, forming at least one electrically conductive element of electrically conductive material through the first insulating layer, the electrically conductive element of electrically conductive material electrically contacting a respective thermoelectric element having the first conductivity type and a respective thermoelectric element having the second conductivity type to interconnect the respective thermoelectric element having the first conductivity type with the respective thermoelectric element having the second conductivity type; and forming one or more second insulating layers of electrically insulating material on the first insulating layer and the at least one electrically conductive element, the first insulating layer comprising the first electrically insulating layer and the one or more second insulating layers of electrically insulating material.

11. The manufacturing method of claim 8, wherein forming the cavity in the substrate comprises: temporarily coupling the thermoelectric unit to a transport wafer, the transport wafer facing the electrically insulating layer of the thermoelectric unit; performing etching at a cavity region of the second surface of the substrate to form the cavity, the cavity region being aligned with the first end of each thermoelectric element along the first direction; and decoupling the thermoelectric unit and the transport wafer from each other.

12. The manufacturing method of claim 8, wherein forming the first thermoplastic layer on the electrically insulating layer is performed by injection molding.

13. The manufacturing method of claim 12, wherein forming the first thermal via in the first thermoplastic layer comprises: forming a first trench in the first thermoplastic layer from the first surface to the second surface of the first thermoplastic layer, the first trench being formed by selectively removing corresponding portions of the first thermoplastic layer with an LDS technique by laser irradiation of a first trench region of the first surface of the first thermoplastic layer, the first trench region being superimposed on the cavity along the first direction; and performing metal deposition in the first trench to form the first thermal via.

14. The manufacturing method of claim 13, wherein the thermoelectric unit comprises a plurality of the thermoelectric elements interconnected to form a serpentine device; the manufacturing method comprising: forming electrically conductive terminals in the electrically insulating layer, the electrically conductive terminals being disposed at end portions of the serpentine device and being exposed by the electrically insulating layer; for each electrically conductive terminal, forming a respective second trench and a respective third trench in the first thermoplastic layer from the first surface of the first thermoplastic layer to the second surface of the first thermoplastic layer, the respective second trench and the respective third trench being arranged laterally with respect to the first trench and being formed by selectively removing respective portions of the first thermoplastic layer with an LDS technique by laser irradiation of a respective second trench region and a third trench region of the first surface of the first thermoplastic layer, the respective second trench region and the third trench region being superimposed on the respective electrically conductive terminal along the first direction, respectively, and being superimposed on the heat spreader laterally extending onto a respective lead wire of the thermoelectric unit, the first thermoplastic layer also being formed on the respective lead wire; for each conductive terminal, chemically activating a respective active area of the first surface of the first thermoplastic layer by laser irradiation with a LDS technique, the respective active area extending between the respective second trench area and third trench area; and performing metal deposition in the second trench and the third trench to form a respective first electrical via and a respective second electrical via, and performing metal deposition on the active area to form a respective electrical connection portion interposed between the respective first electrical via and the respective second electrical via along the second direction, the respective first electrical via, the respective second electrical via, and the respective electrical connection portion together forming a respective electrical connection structure electrically connecting the respective conductive terminal and the respective lead to each other.

15. The manufacturing method of claim 14, comprising forming an insulating layer of insulating material on each of the electrical connection structures.

16. The manufacturing method of claim 15, comprising: forming a second thermoplastic layer on the first thermoplastic layer, on the electrical connection structures, and on the first thermal via by injection molding, the second thermoplastic layer together with the first thermoplastic layer forming the thermoplastic layer; and forming a second thermal via of metallic material in the second thermoplastic layer, the second thermal via overlapping the first thermal via along the first direction.

17. The manufacturing method of claim 8, wherein the thermoelectric unit comprises a plurality of the thermoelectric elements interconnected to form a serpentine device; the manufacturing method comprising, prior to forming the thermoplastic layer on the electrically insulating layer: forming conductive terminals in the electrically insulating layer, the conductive terminals being placed at end portions of the serpentine device and being exposed by the electrically insulating layer; fixing a first end of a respective lead wire to each conductive terminal and fixing a second end of the respective lead wire to a respective lead, the first end and the second end of each lead wire being opposite to each other, each lead extending laterally on the heat sink to the thermoelectric unit; and further forming the thermoplastic layer on the lead wires.

18. A device comprising a thermoelectric unit, the device comprising: a heat sink; the thermoelectric unit having a first surface coupled to the heat sink, the thermoelectric unit comprising: a first substrate portion; a second substrate portion spaced apart from the first substrate portion; an electrically insulating layer extending from the first substrate portion to the second substrate portion, the electrically insulating layer having a first surface opposite to the first surface of the thermoelectric unit along a first direction; a central cavity between the first substrate portion and the second substrate portion, the electrically insulating layer extending over the central cavity; and a plurality of thermoelectric elements in the electrically insulating layer, each thermoelectric element of the plurality of thermoelectric elements comprising a first end and a second end opposite to each other along a second direction transverse to the first direction, and each thermoelectric element being configured to convert a thermal drop between the first end and the second end into an electrical potential between the first end and the second end. ​ a thermoplastic layer over the thermoelectric elements, the thermoplastic layer having a first surface opposite the heat spreader; and a thermal via extending through the thermoplastic layer from the first surface of the thermoplastic layer to the first surface of the electrically insulating layer.

19. The apparatus of claim 18, wherein the first end is over the central cavity and the second end is over the first substrate portion or the second substrate portion.

20. The apparatus of claim 19, wherein the thermal via includes a first end opposite a second end, the first end being on the first surface of the thermoplastic layer and the second end contacting the thermoelectric elements over the first ends of the plurality of thermoelectric elements.

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