Chip for in-plane thermoelectric characterizaton of isotropic and anisotropic films

Abstract

Chip (1) for thermoelectric in-plane characterization of an isotropic or anisotropic film (4), comprising a support structure having at least one bulk (2) and a plurality of suspended membranes (3) supported by the bulk (2), wherein each suspended membrane (3) of the plurality of suspended membranes (3) develops along an in-plane first direction (3a) and is configured to receive the film (4); the chip (1) also comprising, for each suspended membrane (3) of the plurality of suspended membranes (3) at least: a linear heater (5), located along the first direction (3a) of the respective suspended membrane (3); a first electrode (6), located in a central area of the respective suspended membrane (3), and a second electrode (7), located on the bulk (2), outside the respective suspended membrane (3), both the first electrode (6) and the second electrode (7) being aligned along an in-plane second direction (3b) of the respective suspended membrane (3) that is orthogonal to the first direction (3a) and crosses the linear heater (5); two couples of extended contacts (81-82; 83-84), the couples being located on the bulk (2) close to the edges of the respective suspended membrane (3) on opposite sides thereof, parallel to the first direction (3a); a plurality of contact pads (9) and corresponding metal tracks (10), wherein the contact pads (9) are electrically connected by means of the corresponding metal tracks (10) to the linear heater (5), the first electrode (6), the second electrode (7) and the two couples of extended contacts (81-82; 83-84) of the respective suspended membrane (3) of the plurality of suspended membranes (3), and configured to supply input electrical signals thereto or transmit corresponding output electrical signals therefrom, when the film (4) is applied to the suspended membrane (3) and the chip (1) is operatively connected through the contact pads (9), to an external device configured for calculating of the figure of merit of the film (4) along the second direction (3b), based on the output electrical signals transmitted by the contact pads (9); wherein the suspended membranes (3) of the plurality of suspended membranes (3) are supported on the bulk (2) in different positions, so that the figure of merit of the film (4) can be calculated according to the second direction (3b) of each suspended membrane (3) of the plurality of suspended membranes (3), at those positions.

Description

[0001] P1713PC00

[0002] - 1 -

[0003] CHIP FOR IN-PLANE THERMOELECTRIC CHARACTERIZATON OF ISOTROPIC AND ANISOTROPIC FILMS

[0004] ***

[0005] FIELD OF INVENTION

[0006] The present invention relates to a chip for in-plane thermoelectric characterization of isotropic and anisotropic films, more particularly it relates to the complete in-plane thermoelectric characterization of in-plane isotropic and anisotropic thin films and ultra-thin films either grown / deposited conformal or not conformal to the substrate, deposited from solution or grown via vacuum techniques or transferred on the chip.

[0007] BACKGROUD OF THE INVENTION

[0008] Thermoelectric devices, which transform heat into electrical current, are gaining relevance as rapidly evolving renewable energy source. Their energy conversion efficiency depends on the figure of merit zT= oS2T / k where a is the electrical conductivity, S the Seebeck coefficient, k the thermal conductivity of the material and T the temperature. These three parameters that characterize a thermoelectric material are intrinsically related and require to be simultaneously optimized: a high value of S is necessary, which relates to the ability to convert heat into current, a high value of o is also required for the efficient transport of charge, as well as a low value of k, to maintain an optimal temperature gradient.

[0009] Organic semiconductors have emerged as prime candidates for the fabrication of flexible thermoelectric devices, particularly suitable for powering small wearable electronic devices. Known to be non-toxic, economical and easily processable by solution methods and compatible with flexible substrates, they require further optimizations in their thermoelectric properties to compete with alternative energy technologies.

[0010] Recent studies have shown that thermoelectric efficiency is strongly influenced by the presence of in-plane morphological and structural anisotropies in thin films of organic semiconductors, which have demonstrated higher values of electrical conductivity and power factor, compared to their isotropic counterparts. However, reliable techniques for the complete thermoelectric characterization of these anisotropic thin films are still lacking.

[0011] At the same time, two-dimensional materials are gaining interest for their high performance in thermoelectric devices. Their nature as microcrystals with thicknesses of a few atomic layers presents challenges in the thermoelectric characterization, in particular because their growth on substrates of different types is often not conformal, negatively influencing P1713PC00

[0012] - 2 - charge percolation and the formation of effective ohmic contacts.

[0013] This implies the need to fabricate the electrical and thermal contacts on top of the films themselves, a process that increases the complexity and associated costs, and can introduce contamination or defects that might alter the thermoelectric properties of the material.

[0014] Current techniques for the thermoelectric characterization of thin films include:

[0015] -the fabrication of suspended devices, for example as disclosed in Weathers A. etal., "Significant electronic thermal transport in the conducting polymer poly (3, 4-ethylenedioxythiophene)", Advanced Materials, 27(12), 2101-2106, 2015, which requires complex film transfer techniques, introduces significant strain in the suspended films and is not applicable to all materials;

[0016] - the deposition of conductive or insulating layers on top of the film to measure thermal conductivity as disclosed, for example, in Yamaguchi S. et al., "Anisotropic thermal conductivity measurement of organic thin film with bidirectional 3a) method", Review of Scientific Instruments, 92(3), 2021 and Dames, C., "Measuring the thermal conductivity of thin films: 3 omega and related electrothermal methods", Annual Review of Heat Transfer, 16, 2013, with the limitations already mentioned above;

[0017] - the use of optical methods to determine thermal conductivity, as disclosed in Jiang, P. et al., "Tutorial: Time-domain thermoreflectance (TDTR)for thermal property characterization of bulk and thin film materials", Journal of Applied Physics, 124(16), 2018, an indirect measurement technique that requires theoretical models for the analysis of experimental data, and which therefore introduces further variables to the evaluation of thermoelectric parameters;

[0018] - the deposition of the film on suspended membranes equipped with a central heater, as taught in the following articles by Linseis, V. et al., "Advanced platform for the in-plane ZT measurement of thin films", Review of Scientific Instruments, 89(1), 2018; Linseis, V. et al., "Platform for inplane ZT measurement and Hall coefficient determination of thin films in a temperature range from 120 K up to 450 K", Journal of Materials Research, 31, 3196-3204, 2016, Linseis, V. et al., "Complete thermoelectric characterization of PEDOT: PSS thin films with a novel ZT test chip platform", physica status solidi (a), 215(7), 1700930, 2018, and Linseis, V. et al., "Thermoelectric properties of Au and Ti nanofilms, characterized with a novel measurement platform", Materials Today: Proceedings, 8, 517-522, 2019, which for the first time allows a complete characterization of the three thermoelectric parameters of thin films, but requires that the films are conformal to the substrate and isotropic in the in-plane direction.

[0019] To date, there is no platform for the complete characterization of anisotropic and ultra- P1713PC00

[0020] - 3 - thin films grown / deposited non-conformal to the substrate. Moreover, there exist no platform for the evaluation of the anisotropy of the thermal and electrical coefficients in the in-plane direction. Existing techniques for the thermoelectrical characterization of thin films, suitable for isotropic films, introduce large errors and inconsistencies in the evaluation of thermoelectric parameters of anisotropic thin films. Furthermore, for the characterization of anisotropic thin films it is necessary to prepare specific samples for each of the measurements, making it impossible to study all thermoelectric parameters in the same in-plane direction and on the same film, a fundamental condition for a realistic evaluation of the thermoelectric performance of anisotropic thin films.

[0021] Furthermore, by using the prior art techniques there is no possibility to determine the anisotropy of the thermal and electrical conductivity, as well as of the Seebeck coefficients in the plane of the sample for anisotropic thin films.

[0022] Thus, the need is felt to address the above issues, and the main object of the present invention is to allow a simple, accurate, versatile, cheap, and effective thermoelectric characterization of thin and ultra-thin isotropic or anisotropic films, in the in-plane direction, both conformal and non-conformal to the substrate.

[0023] SUMMARY OF THE INVENTION

[0024] It is a specific object of the invention a chip for thermoelectric in-plane characterization of a film, comprising at least one bulk and a plurality of suspended membranes supported by the bulk, wherein each suspended membrane of the plurality of suspended membranes develops along an in-plane first direction and is configured to receive said film; the chip also comprising, for each suspended membrane of the plurality of suspended membranes at least: a linear heater, located along the first direction at the respective suspended membrane, the linear heater being configured to be used to heat and measure the local temperature of the suspended membrane and the stack suspended membrane / film, when the film is applied thereon; a first Seebeck electrode, located in a central area of the respective suspended membrane close to the linear heater so that, in use, the first Seebeck electrode can reach the temperature of the linear heater, and a second Seebeck electrode, located at the bulk, outside the respective suspended membrane, both the first Seebeck electrode and the second Seebeck electrode being aligned along an in-plane second direction of the respective suspended P1713PC00

[0025] - 4 - membrane, that is angularly displaced with respect to the first direction and crosses the linear heater, the first Seebeck electrode and the second Seebeck electrode being configured to be used for measuring the Seebeck coefficient of the film, when the film is applied on their respective suspended membrane; two couples of extended contacts, the couples being located in the bulk close to the edges of the respective suspended membrane on opposite sides thereof, parallel to the first direction and configured to be used for measuring of the electrical conductivity of the film, when the film is applied on the suspended membrane; a plurality of contact pads and corresponding metal tracks located in the bulk, wherein the contact pads of the plurality of contact pads are electrically connected by means of the corresponding metal tracks to the linear heater, the first Seebeck electrode, the second Seebeck electrode and the two couples of extended contacts of the respective suspended membrane of the plurality of suspended membranes, and configured to supply input electrical signals thereto and transmit corresponding output electrical signals therefrom, when the chip is operatively connected through said contact pads to an external device, configured for calculating the figure of merit of the film along the second direction based on the input electrical signals transmitted to and the output electrical signals received from the contact pads; an electrically insulating layer, covering the chip at the bulk, the suspended membranes and the linear heater, except the first and second Seebeck electrodes, the two couples of extended contacts and the plurality of contact pads of the plurality of suspended membranes; wherein the suspended membranes of the plurality of suspended membranes are supported on the bulk in different positions, so that when the film is applied on the suspended membrane, the figure of merit of the film can be calculated according to the second direction of each suspended membrane of the plurality of suspended membranes, at those positions.

[0026] According to an aspect of the invention, at least two suspended membranes (3) of the plurality of suspended membranes (3) can be angularly displaced with respect to one another and the displacement angle therebetween can be comprised between 0° and 360° enabling the estimation of the anisotropy in the thermal and electrical conductivity as well as of the Seebeck coefficient and figure of merit zT in the in-plane direction.

[0027] According to another aspect of the invention, in the bulk at least one recess can be obtained, between the plurality of contact pads and at last one suspended membrane of the plurality of suspended membranes. P1713PC00

[0028] - 5 -

[0029] Accordingto a further aspect of the invention the metal tracks can be located on the bulk or the plurality of suspended membranes.

[0030] According to another aspect of the invention, the metal tracks can be partially or fully embedded in the bulk or in the plurality of suspended membranes.

[0031] According to a further aspect of the invention, the contact pads can be located on the bulk on a face thereof supporting the plurality of suspended membranes.

[0032] According to still another aspect of the invention, the contact pads can be located on the bulk on a face thereof different from the one supporting the plurality of suspended membranes, optionally a face opposite to the face of the bulk supporting the plurality of suspended membranes.

[0033] According to another aspect of the invention, the linear heater can be an extension of the corresponding metal track configured to supply input electrical signals thereto and transmit corresponding output electrical signals therefrom.

[0034] According to a further aspect of the invention, the chip can comprise two suspended membranes angularly displaced with respect to one another according to a displacement angle of 45° or 90°.

[0035] According to still another aspect of the invention, the suspended membranes can have a polygonal plan configuration, optionally a square or rectangular one, or a circular configuration.

[0036] According to another aspect of the invention, at least one recess can protect the contact pads from the formation of the film when the film is prepared by solution processing techniques.

[0037] According to a further aspect of the invention, all the thermoelectric parameters of the figure of merit can be measured along the exact same direction and with a spatial resolution, defined by the membrane area.

[0038] BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present invention will be now described, by way of illustration and not by way of limitation, according to its preferred embodiments, with particular reference to the attached Figures, wherein:

[0040] Fig. 1 shows a schematic plan view of the chip according to a preferred embodiment of the invention;

[0041] Fig. la is a schematic plan view of one variation of the chip depicted in Fig. 1;

[0042] Fig. 2 represents an enlarged scale view detail of the invention chips of Figs. 1 and la;

[0043] Fig. 3 shows a cross-sectional view of the invention chip configuration, taken along P1713PC00

[0044] - 6 - section line Ill-Ill of Fig. 1;

[0045] Fig. 4 is one variation of the cross-sectional view of the chip configuration, of Fig. 3;

[0046] Fig. 5 represents another variation of the cross-sectional view of the chip configuration of Fig. 3;

[0047] Fig. 6 shows a schematic representation of the invention chip according to another embodiment of the invention; and

[0048] Fig. 7 is a schematic representation of the of the invention chip according to another embodiment of the invention.

[0049] In the Figures identical reference numerals will be used for alike elements.

[0050] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0051] With particular reference to the enclosed Figures, it will be appreciated that a chip for in-plane thermoelectric characterization of an isotropic or anisotropic film, according to the present invention is generally referred to with reference numeral 1 and comprises at least one bulk 2, and a plurality of plane suspended membranes 3 supported by the bulk 2.

[0052] In the chip 1 of the invention, each suspended membrane 3 of the plurality of suspended membranes 3 is configured to receive a film 4 (see Figs 3 to 5), for example a thin or an ultrathin film made of an organic or inorganic semiconductor, for the in-plane thermoelectric characterization thereof. According to a preferred embodiment of the invention, the bulk 2 is a silicon bulk even though the skilled person will have no difficulty in understanding that other suitable materials, for example Ge or fused silica, etc. could be used. The suspended membranes 3 of the plurality of membranes are made of SiO2 / SiN / SiO2. Again, the skilled person will have no difficulty in understanding that other suitable materials, for example insulating materials with low thermal conductivity, such as AI2O3, TiCh, etc. could be used.

[0053] Each suspended membrane 3 of the plurality of suspended membranes defines a first direction 3a and a second direction 3b, which are angularly displaced with respect to each other, optionally orthogonal to each other, and represent one in-plane development direction of the suspended membrane 3 supported by the bulk 2, and the in-plane measurement direction of the thermoelectric parameters of the film 4 that the suspended membrane 3 is configured to receive, respectively. Each suspended membrane 3 has a polygonal plan configuration, optionally a square or rectangular one. In the Figures, for simplicity, rectangular suspended membranes 3 have been represented, wherein the first direction 3a represents the main development in-plane direction of each suspended membrane 3. On the other hand, the P1713PC00

[0054] - 7 - direction 3b is the only one along which all the thermoelectric parameters of both isotropic or anisotropic thin films are measured.

[0055] According to the invention, for each suspended membrane 3 of the plurality of suspended membranes, the chip 1 comprises:

[0056] - a linear heater 5, optionally comprising a linear metal track, that is arranged along the first direction 3a at the respective suspended membrane 3,

[0057] - a first Seebeck electrode 6, located in a central area of the respective suspended membrane 3 close to the liner heater 5, so that, in use, the first electrode 6 can be brought at the same or very similar temperature of the linear heater 5, and

[0058] - a second Seebeck electrode 7, located at the bulk 2, outside the respective suspended membrane 3.

[0059] Both the first electrode 6 and the second electrode 7 are aligned along the second direction 3b of the respective suspended membrane 3, which crosses the linear heater 5.

[0060] The chip 1 according to the invention also comprises, for each suspended membrane 3 of the plurality of suspended membranes 3, two couples of extended contacts (81-82, 83-84 in Figs 1 and 2), the couples being located on the bulk 2, close to the edges of the respective suspended membrane 3 on opposite sides thereof and parallel to the first direction 3a of the same. Optionally, the extended contacts 81-82, 83-84 can also be placed on the suspended membrane 3, each couple of contacts being placed on one side with respect to the linear heater 5 and first Seebeck electrode 6, again parallel to the second couple.

[0061] In Figures 1 and 2, both of the two couples of extended contacts (81-82; 83-84) are represented closer to the respective suspended membrane 3 than the second Seebeck electrode 7. However, according to one variation of the invention, the second Seebeck electrode 7 can be arranged closer to the respective suspended membrane 3 than one or both of the two couples of extended contacts (81-82; 83-84), as long as the second Seebeck electrode 7 is on the bulk 2.

[0062] The chip 1 of the invention furthermore comprises, for each suspended membrane 3 of the plurality of suspended membranes, a plurality of contact pads 9 (namely twelve contact pads for each suspended membrane 3) and corresponding metal tracks 10, optionally made of or comprising Pt or Au, located in the bulk 2, the contact pads 9 being electrically connected by means of the metal track 10 at least to some of the following: the linear heater 5, the first Seebeck electrode 6, the second Seebeck electrode 7 and the two couples of extended contacts (81-82; 83-84) of the respective suspended membrane 3, and configured for supplying suitable P1713PC00

[0063] - 8 - input electrical signals thereto and transmitting corresponding output electrical signals therefrom, when the chip 1 is operatively connected through the contact pads 9 to an external device configured for calculating the figure of merit of the film 4 along the second direction 3b, based on the input electrical signals transmitted to and the output electrical signals received from the contact pads 9.

[0064] In fact, each linear heater 5 is configured to be used as a thermometer, to measure the local temperature increase of the respective suspended membrane 3 and of the film / suspended membrane stack, after the film 4 is applied thereon. For example, with the linear heater 5 being a metal track, optionally an extension of the corresponding metal track 10 connected thereto, the local variation of the temperature at the center of the membrane could be obtained by providing a corresponding current input electrical signal to the linear heater 5 and based on the temperature coefficient of resistance (TCR) of the metal, which has previously been determined for the metal making up the metal track 10, with standard techniques. The first Seebeck electrode 6 and second Seebeck electrode 7 of a respective suspended membrane 3 are configured to be used for measuring of the Seebeck coefficient of the film 4, when the film 4 is applied on that suspended membrane 3, based on the voltage difference dV between the first Seebeck electrode 6 and the second Seebeck electrode 7 as a function of the temperature variation dT between the same electrodes (induced by the passage of current in the linear heater 5) according to the formula S=dV / dT. The two couples of extended contacts (81-82; 83-84) of each suspended membrane 3 of the plurality of suspended membranes 3 are configured to be used for measuring the electrical conductivity of the film 4, when it is applied on the respective suspended membrane 3, in the region of the suspended membrane 3 itself and in the same second direction 3b according to which the Seebeck coefficient and the thermal conductivity are measured. Indeed, to avoid short circuits a passivation layer made of an insulating material, or another suitable dielectric film, is deposited on the entire surface of the chip with the exception of the first Seebeck electrode 6, the second Seebeck electrode 7, the contact pads 9 and the two couples of extended contacts (81-82; 83-84) in the region where the contacts are parallel to the first direction 3a of each membrane 3.

[0065] According to an aspect of the invention, the suspended membranes 3 of the plurality of suspended membranes 3 are supported on the bulk 2 in different positions, so that the figure of merit of the film (when applied on the chip) can be calculated according to the second direction 3b of each suspended membrane 3, at those different positions, where the deposited film can P1713PC00

[0066] - 9 - be possibly treated in different manners.

[0067] According to an advantageous embodiment of the invention, at least two suspended membranes 3 of the plurality of suspended membranes 3 can be angularly displaced with respect to one another and the displacement angle therebetween is comprised between 0° and 360°, being it possible that other suspended membranes 3 of the plurality of suspended membranes 3 are supported on the bulk 2 parallel with each other, i.e. according to the same first direction 3a and second direction 3b. With such a configuration, the skilled person will understand that in case the film 4 supported by the plurality of suspended membranes 3 is anisotropic, it is possible to determine for each direction 3b of each membrane 3 the entire set of thermoelectric parameters o, S, and k along that direction, and also the anisotropy coefficients in the in-plane directions of the thermal and electrical conductivity and of the Seebeck coefficient along the different second directions 3b of the respective suspended membranes 3.

[0068] Advantageously, in the bulk 2 of the chip 1 according to the invention, at least one recess 11 is obtained, between the plurality of contact pads 9 and the plurality of suspended membranes 3. In Figs 1, 2 and 6, for example, the contact pads 9 are located close to the edges of the bulk 2 and four (4) recesses 11, two for each suspended membrane 3, are obtained for physically insulating the contact pads 9 from the suspended membranes 3 while keeping the electrical connections. In Fig 7, instead, the contact pads 9 are still located close to the edges of the bulk 2 and four (4) recesses 11, one for each suspended membrane 3, are obtained for separating the contact pads 9 from the suspended membranes 3. It will be noted that in the Figs, the recesses 11 are L-shaped. However, the skilled person will have no difficulty in understanding how recesses 11 could also have a different shape, for example a curved shape, as long as they are located between the plurality of contact pads 9 and the plurality of suspended membranes 3.

[0069] The presence of the recesses 11 is advantageous because it helps improving the homogeneity of the thin film 4 under investigation, when it is applied on the chip 1. In fact, it is difficult to homogeneously deposit thin films from solution only on the active area of the chip and excluding the contact pads to prevent the occurrence of short circuits. The traditional use of an adhesive tape on the contact pads to mask them before deposition of the film produces, in fact, accumulations of material at the edges of the subsequently removed tape. Not only that, the removal of the film from the contact pads 9 via plasma, using a mask to protect the region of interest of the film, introduces the risk of underetching or modification of the deposited film, P1713PC00

[0070] - 10 - increases the film temperature resulting in unwanted film annealing and increases the preparation time of the film before the thermoelectrical characterization. With the invention chip 1, instead, when the films are deposited from a solution, the recesses prevent the solution from reaching the contact pads 9, thereby easily avoiding the creation of short circuits without the need for any post-treatment of mechanical / plasma removal of the deposited film from the contact pads 9.

[0071] According to another embodiment of the invention and as anticipated above, see Figs 3 to 5, the chip 1, is covered with an electrically insulating layer 12, for example made of or comprising SiO2, SigNzi, AI2O3, TiO2 or any other suitable dielectric material, except for the first electrode 6 and second electrode 7, the two couples of extended contacts (81-82; 83-84) in the region where these are parallel to the second membrane direction 3b of the corresponding membrane 3, and the plurality of contact pads 9 for charge injection and signal reading, for each suspended membrane 3 of the plurality of suspended membranes. With this configuration, good electrical contacts between the film 4 (when it is applied on the chip 1 of the invention), the Seebeck electrodes 6 and 7, the extended contacts (81-82; 83-84) and the contact pads 9 is obtained in each suspended membrane 3.

[0072] Furthermore, the metal tracks 10 can be obtained on the bulk 2 or on the plurality of suspended membranes 3. However, alternatively, they can also be partially or fully embedded in the bulk 2 and / or in the plurality of suspended membranes 3. This is advantageous because it allows the in-plane thermoelectric characterization of ultrathin films, that are not conformal to the surface of the chip 1, given that the deposition of 2D materials with micrometric or sub micrometric dimensions and thicknesses of a few nanometers does not adapt to the topography of the chip, in case it has metal tracks 10 and contacts that have a thicknesses that is in the same order of magnitude or orders of magnitude larger.

[0073] According to another preferred embodiment of the invention, the contact pads 9 can be located on the bulk 2 on a face thereof wherein the plurality of suspended membranes 3 are supported and / or on a face thereof different from the one supporting the plurality of suspended membranes 3, optionally, the face of the bulk 2 opposite to the one supporting the plurality of suspended membranes 3. For example, at least part of the contact pads 9 can be located on the bulk 2 face wherein the plurality of suspended membranes 3 are supported and the remaining part can be located on the face thereof opposite to the one supporting the plurality of suspended membranes 3. P1713PC00

[0074] - 11 -

[0075] The configuration of Fig. la, wherein all contact pads 9 are located on the bulk 2 face opposite to the one supporting the plurality of suspended membranes 3, can be advantageous because it prevents the film 4 deposited (from solution, in vacuum or by transfer) on the invention chip 1, to come into contact with the contact pads 9.

[0076] The film 4 to be thermoelectrically characterized with the chip 1 of the present invention can be applied on the plurality of suspended membranes 3 from solution, in vacuum or by transfer and the thermoelectrical characterization can be carried out at atmospheric pressure or in vacuum.

[0077] For an accurate characterization of a film 4 thermal conductivity, the invention chip 1 must operate in vacuum to reduce thermal losses, at a pressure < 10'2mbar, preferably in high vacuum at a pressure < 10‘5mbar.

[0078] The chip 1 is therefore configured to be inserted into a vacuum chamber to allow thermoelectric measurements in high vacuum. To be inserted into the vacuum chamber, the invention chip 1 is configured to be connected to a base that allows the passage of electrical signals from the chip to an external device used for this purpose, and vice versa. Alternatively, the chip can be attached to a flange equipped with electrical pins, each electrical pin contacting one of the chip contact pads 9. However, the skilled person will easily understand that other configurations are possible as long as the electrical connection between the invention chip 1 within the vacuum chamber and an external device configured for calculating the figure of merit of the film 4 is maintained, as well as the vacuum inside the vacuum chamber.

[0079] It should be noted that with such a configuration of the invention chip 1, in order to improve the accuracy of the thermal conductivity measurement, the thermal resistance of each suspended membrane 3 can be determined in high vacuum before deposition of the film 4 on the suspended membranes 3 themselves, and its contribution subtracted from the thermal resistance of the film / membrane stack, measured at the same pressure or in the same pressure range, in order to obtain the thermal conductivity contribution of the film alone by subtracting the contribution of the bare membrane.

[0080] The chip 1 according to the invention reaches the goals disclosed in the preamble above. In fact, thanks to its configuration and the presence of the plurality of suspended membranes, it allows the complete thermoelectrical characterization of thin films that are both isotropic and anisotropic in the plane of the film, along one and the same identical direction in the plane of the film, optionally along a different direction per each membrane, optionally using the known P1713PC00

[0081] - 12 -

[0082] 3w technique or the steady-state linear heater 5 in a complete, rapid manner and without any further manufacturing step, required after the deposition of the film 4 under investigation.

[0083] With the invention chip 1 it is possible to simultaneously measure the thermal and electrical conductivity and the Seebeck coefficient in the same or two or more different directions as desired (orthogonal or not) of the exact same thin film, thereby providing the unique possibility of extracting the thermal, electrical and Seebeck anisotropy coefficients of the film in the plane.

[0084] The invention chip 1 also allows measuring all three thermoelectric parameters with excellent spatial localization in the same region of the chip, identified by the position of the suspended membranes 3. It also avoids the problems described above associated with the process of masking the contact pads 9 before deposition of the film 4, or with the mechanical or plasma removal of the deposited film 4 therefrom, to avoid short circuits. The recesses 11 also provide to possibility of avoiding the problems described above associated with the process of masking the electrical pads before deposition of the film 4, when the film 4 is deposited on the invention chip 1 from a solution.

[0085] The invention chip also allows to carry out a complete thermoelectric characterization for thin films both conformal and non-conformal to the substrate, possibly using metal tracks 10 and electrodes embedded or partially embedded in the suspended membranes 3 and in the chip 1.

[0086] The preferred embodiments of this invention have been described and a number of variations have been suggested hereinbefore, but it should be understood that those skilled in the art can make other variations and changes without so departing from the scope of protection thereof, as defined by the attached claims.

[0087] For example, in the description above, the suspended membranes 3 have been described as having a polygonal, optionally square or rectangular shape. However, in case the invention chip 1 is used for the in-plane characterization of an isotropic film 4, the suspended membranes could also be circular.

Claims

P1713PC00- 13 -CLAIMS1. Chip (1) for thermoelectric in-plane characterization of a film (4), comprising at least one bulk (2) and a plurality of suspended membranes (3) supported by the bulk (2), wherein each suspended membrane (3) of the plurality of suspended membranes (3) develops along an inplane first direction (3a) and is configured to receive said film (4); the chip (1) also comprising, for each suspended membrane (3) of the plurality of suspended membranes (3) at least: a linear heater (5), located along the first direction (3a) at the respective suspended membrane (3), the linear heater (5) being configured to be used to heat and measure the local temperature of the suspended membrane (3) and the stack suspended membrane (3) / film (4), when the film (4) is applied thereon; a first Seebeck electrode (6), located in a central area of the respective suspended membrane (3) close to the linear heater (5) so that, in use, the first Seebeck electrode (6) can reach the temperature of the linear heater (5), and a second Seebeck electrode (7), located at the bulk (2), outside the respective suspended membrane (3), both the first Seebeck electrode (6) and the second Seebeck electrode (7) being aligned along an in-plane second direction (3b) of the respective suspended membrane (3), that is angularly displaced with respect to the first direction (3a) and crosses the linear heater (5), the first Seebeck electrode (6) and the second Seebeck electrode (7) being configured to be used for measuring the Seebeck coefficient of the film (4), when the film (4) is applied on their respective suspended membrane (3); two couples of extended contacts (81-82; 83-84), the couples being located in the bulk (2) close to the edges of the respective suspended membrane (3) on opposite sides thereof, parallel to the first direction (3a) and configured to be used for measuring of the electrical conductivity of the film (4), when the film (4) is applied on the suspended membrane (3); a plurality of contact pads (9) and corresponding metal tracks (10) located in the bulk (2), wherein the contact pads (9) of the plurality of contact pads (9) are electrically connected by means of the corresponding metal tracks (10) to the linear heater (5), the first Seebeck electrode (6), the second Seebeck electrode (7) and the two couples of extended contacts (81-82; 83-84) of the respective suspended membrane (3) of the plurality of suspended membranes (3), and configured to supply input electrical signals thereto and transmit corresponding output electrical signals therefrom, when the chip (1) is operatively connected through said contact pads (9) toP1713PC00- 14 - an external device, configured for calculating the figure of merit of the film (4) along the second direction (3b) based on the input electrical signals transmitted to and the output electrical signals received from the contact pads (9); an electrically insulating layer (12), covering the chip (1) at the bulk (2), the suspended membranes (3) and the linear heater (5), except the first and second Seebeck electrodes (6,7), the two couples of extended contacts (81-82; 83-84) and the plurality of contact pads (9) of the plurality of suspended membranes (3); wherein the suspended membranes (3) of the plurality of suspended membranes (3) are supported on the bulk (2) in different positions, so that when the film (4) is applied on the suspended membrane (3), the figure of merit of the film (4) can be calculated according to the second direction (3b) of each suspended membrane (3) of the plurality of suspended membranes (3), at those positions.

2. Chip (1) according to claim 1, wherein at least two suspended membranes (3) of the plurality of suspended membranes (3) are angularly displaced with respect to one another and the displacement angle therebetween is comprised between 0° and 360° enabling the estimation of the anisotropy in the thermal and electrical conductivity as well as of the Seebeck coefficient and figure of merit zT in the in-plane direction.

3. Chip (1) according to claim 1 or 2, wherein in the bulk (2) at least one recess (11) is obtained, between the plurality of contact pads (9) and at last one suspended membrane (3) of the plurality of suspended membranes (3).

4. Chip (1) according to any previous claim, wherein the metal tracks (10) are located on the bulk (2) or the plurality of suspended membranes (3).

5. Chip (1) according to any claim 1 to 3, wherein the metal tracks (10) are partially or fully embedded in the bulk (2) or in the plurality of suspended membranes (3).

6. Chip (1) according to any previous claim, wherein the contact pads (9) are located on the bulk (2) on a face thereof supporting the plurality of suspended membranes (3).

7. Chip (1) according to any previous claim, wherein the contact pads (9) are located on the bulk (2) on a face thereof different from the one supporting the plurality of suspended membranes (3), optionally a face opposite to the face of the bulk (2) supporting the plurality of suspended membranes (3).

8. Chip (1) according to any previous claim, wherein the linear heater (5) is an extension of the corresponding metal track (10) configured to supply input electrical signals thereto andP1713PC00- 15 - transmit corresponding output electrical signals therefrom.

9. Chip (1) according to any previous claim, comprising two suspended membranes (3) angularly displaced with respect to one another according to a displacement angle of 45° or 90°.

10. Chip (1) according to any previous claims, wherein the suspended membranes (3) have a polygonal plan configuration, optionally a square or rectangular one, or a circular configuration.

11. Chip (1) according to any previous claim, wherein at least one recess (11) protect the contact pads (9) from the formation of the film when this is prepared by solution processing techniques.

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