Energy generation module comprising transducer of temperature changes into electricity, set of modules, and use thereof

Abstract

The object of the invention is an energy generation module comprising a transducer of temperature changes into electricity, characterized in that it comprises a bistable membrane (1) susceptible to deformation upon a change of temperature over time, with an undulated shape, the module further comprising cavities (5a) and (5b), which are connected with each other by a tunnel located under the bistable membrane (1), that is supported at both opposite ends of the tunnel, so that the bottom of the tunnel constitutes the substrate silicon layer (3), while the ceiling of the tunnel constitutes the bistable membrane (1). A further object of the invention is a set of modules connected in series or in parallel, as well as the use thereof for powering loT network nodes.

Description

[0001] Energy generation module comprising transducer of temperature changes into electricity, set of modules, and use thereof

[0002] The invention relates to an energy generation module comprising a transducer of temperature changes into electricity a set of modules, and the use thereof for powering loT network nodes.

[0003] Various microtransducers incorporating piezoelectric materials for converting energy in one form into useful energy in another form are disclosed in W02002084754. In one embodiment, a piezoelectric microtransducer can function either as a thermal microengine, converting thermal energy into electrical energy, or as a thermal micropump, consuming electrical energy to transfer thermal energy from a low-temperature heat source to a high- temperature radiator. In another embodiment, the piezoelectric microtransducer is used to convert the kinetic energy of an oscillating or vibrating body, on which the microtransducer is disposed, into useful electrical energy. The piezoelectric microtransducer is also used to extract work from a pressurized fluid stream. A combustion microengine and a Rankine- cycle thermal microengine have also been disclosed, wherein a single fluid acts as the working fluid and the fuel.

[0004] JP2009165931 discloses a method for manufacturing a capacitive ultrasonic transducer, which improves mechanical properties of the membrane and the performance while suppressing the increase in parasitic capacitance. The manufacturing method for the capacitive ultrasonic transducer includes the following steps: preparing a Silicon On Insulator (SOI) substrate having an active layer on a carrier substrate separated by an insulating layer; forming a through-hole in the active layer or the carrier substrate; forming a cavity by introducing an insulating layer etching fluid through the through-hole formed in the active layer or the carrier substrate and etching the insulating layer; forming an insulating film inside the cavity created by etching the insulating layer; and sealing the through-hole after forming the insulating film inside the cavity.

[0005] The solution described in application EP22461520 represents an energy generation module capable of converting pressure changes into electrical energy. It comprises a pressure transducer with a cavity and a membrane that can deform due to the pressure difference between the fluid inside and outside the cavity. A piezoelectric element that can convert the membrane's motion energy into electrical energy is also connected to the pressure transducer. The cavity is sealed, and the membrane is selected so as to respond to daily changes in atmospheric pressure. The piezoelectric element consists of multiple elongated elements arranged in space, capable of engaging with the pressure transducer. When the pressure change exceeds a predetermined value, the release of the energy occurs.

[0006] Numerous piezoelectric materials and structures, as well as appropriate energy harvesting methods, have been disclosed in Safaei, M. et al., "A review of energy harvesting using piezoelectric materials: state-of-the-art a decade later (2008-2018)." Smart Materials and Structures 28 (2019): 113001. It is emphasized that environmental energy is generally available in the form of solar energy, thermal energy, electromagnetic waves, and vibrational energy. Among these energy sources, vibrational energy is consistently present in nature and human-made structures. Various materials and transduction mechanisms are capable of converting vibrational energy into useful electrical energy, such as piezoelectric, electromagnetic, and electrostatic generators. Energy harvesting from vibrations using piezoelectric transducers has been extensively studied due to their inherent simplicity, considerable power density, and simple design as compared to electrostatic or electromagnetic transducers.

[0007] The possibility of harvesting energy from atmospheric fluctuations was discussed in Gibran Ali, John Wagner, David Moline, Todd Schweisinger, Energy harvesting from atmospheric variations - Theory and test, Renewable Energy, Volume 74, 2015, Pages 528- 535, ISSN0960-1481, h ttp s 7 / doi . org / 10. 1016 / i .ren en e .2014.08.033. The approach is based on daily temperature fluctuations, with an assumed change of 23°C. Such high fluctuations are not always available. Atmospheric pressure also exhibits certain daily fluctuations, which depend on the geographical region - Blancq, Frank. (2011). Daily variability of pressure: The atmospheric tide, Weather, Volume 66, Pages 306-307, 2011, ISSN1477-8696,

[0008] Often recognized and utilized types of environmental energy, such as vibrational, solar, or wind energy, are not always available in all locations and at all times. Consequently, the potential of energy derived from daily atmospheric pressure changes has been noted. Unfortunately, while this type of energy is commonly available, its quantity is relatively low, and the harvesting and effective utilization of this energy source is a challenge. To design an energy-generating module based on this source, it is essential to adapt it for large-scale component manufacturing and to address difficulties associated with the low levels of this type of energy.

[0009] The potential of energy resulting from daily temperature changes is also highly interesting. Unfortunately, although this form of energy is widely available, its quantity is relatively low. Therefore, harvesting and effective use of this energy source represents a great challenge. An equally important technical problem is the construction of modules capable of connecting with each other, thereby enabling efficient conversion of energy arising from temperature changes.

[0010] The aim of the invention was to develop an energy generation module due to temperature changes.

[0011] The object of the invention is an energy generation module comprising a transducer of temperature changes into electricity, characterized in that it comprises a substrate, which constitutes a substrate silicon layer coated with a buried oxide layer. On the buried oxide layer a bistable membrane is placed that is susceptible to deformation upon change of temperature over time. An important disadvantage of spherical-shape membranes is that an increase in temperature leads only to stronger concaving of the dome, instead of a switch from the concave (dome) to a convex (bowl) state. Due to that, the membrane has an adequately designed undulated shape which allows obtaining the bistability effect of the membrane. Furthermore, on the bistable membrane a piezoelectric layer is disposed, on which a metal electrode is disposed, and simultaneously, on the metal electrode a first electrical contact is disposed. Furthermore, the module comprises two cavities which are connected with each other by a tunnel located under the bistable membrane, such that the bottom of the tunnel constitutes the substrate silicon layer, whereas the ceiling of the tunnel constitutes the bistable membrane. The module comprises also a third cavity in which a second electrical contact is disposed on the membrane. It is important for the difference of the thermal expansion coefficients of the bistable membrane, the metal electrode layer, and the piezoelectric layer to be at least three-fold.

[0012] Preferably, the bistable membrane is a silicon membrane.

[0013] Preferably, the bistable membrane is a heavily doped silicon layer and is made using the SOI technology.

[0014] Optionally, the bistable silicon membrane is coated with a thin metal layer to reduce the series resistance of the silicon layer.

[0015] Preferably, the bistable membrane is made of a metal selected from the group including aluminum, titanium, tungsten, copper, or a highly conductive material selected from the group including TiN (titanium nitride) and TaN (tantalum nitride). Other metals and compounds can equally be used to make the bistable membrane, provided that the minimum difference of the thermal expansion coefficients of the bistable membrane layer, the metal electrode layer, and the piezoelectric layer is observed. Preferably, the bistable membrane has a length ranging from 20 gm to 20 mm, most preferably 1 mm.

[0016] Preferably, the piezoelectric layer is made from a material selected from the group including ZnO, PZT (lead zirconate titanate), PVDF (polyvinylidene fluoride) and its copolymers, BaTiCh, LiNbCh or quartz silicate. Other materials can equally be used to make the piezoelectric layer, provided that the minimum difference of the thermal expansion coefficients of the bistable membrane layer, the metal electrode layer, and the piezoelectric layer is observed.

[0017] Preferably, the piezoelectric layer is made of PVDF.

[0018] Preferably, the piezoelectric layer thickness is 10-1000000 nm.

[0019] Preferably, the metal electrode is made of aluminum.

[0020] Preferably, the metal electrode thickness is within the range 15-1000000 nm.

[0021] An object of the invention is also a set of modules, as defined above, connected in series or in parallel.

[0022] An object of the invention is also the use of the set of modules, as defined above, for powering loT network nodes.

[0023] The advantage of the present invention is that, although the energy supplied by the module according to the invention is not sufficient for many traditional applications, it is adequate for numerous Internet of Things (loT) applications, which require small doses of energy delivered in peaks concentrated within narrow time intervals, as discussed in: Maciej Haras, Thomas Skotnicki, Thermoelectricity for loT - A review, Nano Energy, Volume 54, Pages 461-476, 2018, ISSN 2211-2855, htips. / / doi .org / 10.1016Zj.nanoen.2018.10.013.

[0024] The object of the invention in an example embodiment is shown in the drawing, where: Fig. 1 schematically shows the module according to the invention in a cross-sectional view; Fig. 2 schematically shows the module according to the invention in a top view;

[0025] Fig. 3(a) shows the shape of the concave bistable membrane that additionally comprises two bulges on both sides at 15.5 °C. The total length of the membrane is 1 mm, the thickness is 5 gm, the length of the flat section of the membrane in its central part is 0.2 mm, the total length of both arched sides is 0.8 mm, and the depth of the central point in the neutral position is 40 pm. The horizontal axis represents the length of the membrane in mm, while the vertical axis represents the amount of displacement in mm. Displacement is defined as the deviation of the central point from the initial state. Fig. 3(b) shows the switch of the membrane shown in Fig. 3(a) at 16 °C. The horizontal axis represents the length of the membrane in mm, while the vertical axis represents the amount of displacement in mm.

[0026] Fig. 3(c) shows the result of a COMSOL simulation for the membrane shown in Figs. 3(a) and 3(b). The horizontal axis represents temperature changes expressed in °C, while the vertical axis represents the amount of displacement in pm.

[0027] Fig. 4(a) shows the shape of the concave bistable membrane that additionally comprises two bulges on both sides at 24.4 °C. The total length of the membrane is 1 mm, the thickness is 15 pm, the length of the flat section of the membrane in its central part is 0.2 mm, the total length of both arched sides is 0.8 mm, and the depth of the central point in the neutral position is 40 pm. The horizontal axis represents the length of the membrane in pm, while the vertical axis represents the amount of displacement in pm.

[0028] Fig. 4(b) shows the switch of the membrane depicted in Fig. 4(a) at 25 °C. The horizontal axis represents the length of the membrane in pm, while the vertical axis represents the amount of displacement in pm.

[0029] Fig. 4(c) shows the result of a COMSOL simulation for the membrane shown in Figs. 4(a) and 4(b). The horizontal axis represents temperature changes expressed in °C, while the vertical axis represents the amount of displacement in pm.

[0030] Fig. 5(a) shows the shape of the concave bistable membrane that additionally comprises two bulges on both sides at 52 °C. The total length of the membrane is 1 mm, the thickness is 30 pm, the length of the flat section of the membrane in its central part is 0.2 mm, the total length of both arched sides is 0.8 mm, and the depth of the central point in the neutral position is 40 pm. The horizontal axis represents the length of the membrane in pm, while the vertical axis represents the amount of displacement in pm.

[0031] Fig. 5(b) shows the switch of the membrane shown in Fig. 5(a) at 53 °C. The horizontal axis represents the length of the membrane in pm, while the vertical axis represents the amount of displacement in pm.

[0032] Fig. 5(c) shows the result of a COMSOL simulation for the membrane shown in Figs. 5(a) and 5(b). The horizontal axis represents temperature changes expressed in °C, while the vertical axis represents the amount of displacement in pm.

[0033] Fig. 6 shows example undulations obtained using two tensile stressors and one compressive stressor; (a) shows the state before the release of the stressors; (b) shows the state after the release of the stressors. Fig. 7(a-c) shows another method of obtaining undulation in the bistable membrane, step (a) shows resist domes after thermal resist flossing process (resist flossing); step (b) shows the resist domes coated with metal etched into elongated strips; step (c) shows the elongated metal strips released by etching away from the resist.

[0034] Fig. 8 shows a simplified diagram - a matrix of two SFINKS connected in parallel in a top view.

[0035] Fig. 9 shows embodiments of matrixes for arrangements of unconnected modules , i.e., each cell is isolated from the others using MESA isolation, i.e. an island delimited by etched phases in layers 6, 7, and 1, with etching stopping at layer 2.

[0036] Module realisation - General Information

[0037] The process of production of the energy generation module using the SOI (Silicon on Insulator) technology includes the use of advanced LSI (Large Scale of Integration) microelectronic engineering techniques. The process begins with the preparation of a monocrystalline silicon (Si) substrate of proper orientation.

[0038] An insulating layer (e.g., silicon dioxide, SiO?) is deposited onto the substrate, typically through a thermal oxidation process.

[0039] Subsequent layers are formed using well-known techniques “wafer-bonding” and “smart-cut”, developed, for instance, by Soitec.

[0040] The SOI layer is then subjected to heavy doping (n+ or p+ type) using doping techniques well-known in the art (e.g., ion implantation, plasma doping, or exo-diffusion from boron or phosphorus glasses). This aims at imparting the SOI layer with properties of an electrode (i.e., very high conductivity). Optionally, for improved electrode performance, the SOI layer may be coated with a thin metal layer (not shown in the drawings) before applying the piezoelectric layer.

[0041] In the next step, the piezoelectric layer, such as a PVDF layer (alternatively, it can be another piezoelectric material layer, e.g., ZnO, PZT, etc.) is deposited, followed by a metal electrode layer deposited thereon.

[0042] Subsequently, a window for a contact (10) is etched in the metal layer (6) and the piezoelectric layer (7), and the etching of this window is selective and stops at the SOI membrane layer (1). The membrane that reacts to the temperature changes is carefully designed and isolated from the active layer. Through successive photolithography and etching steps, at least two cavities bounded by the membrane are formed, under which a clearance connecting the two cavities is created via isotropic etching of SiO?, selective with respect to silicon, what aim to etch the clearance in the buried oxide (2) without compromising the integrity of the substrate silicon layer (3) and the SOI layer (1). Here, the cavity shape is tailored to the required geometry and volume to ensure that the membrane, in its concave arch position, does not touch the bottom of the cavity. The clearance serves the purpose of etching the buried oxide (BOX) under the membrane, to enable the up-and- down movement of the membrane.

[0043] Then the module undergoes multi-stage testing, including, but not limited to, measurements of membrane deformations in response to temperature changes. Upon completing all production steps, the module undergoes final testing to confirm compliance with expectations. In case of the positive results, the process moves on to mass production.

[0044] In the discussed process, use of the SOI technology allows for precise isolation of layered structures, which is critical for complex microelectronic systems such as the described energy generation module.

[0045] Membrane

[0046] The term "bistable membrane" refers to a membrane structure that has two stable deformation states, which is known as bistability. A bistable membrane has two equivalent and stable deformation states. This means that it can remain in two different states depending on environmental conditions or external stimuli. In this invention, the bistable membrane has an undulated shape. As demonstrated in the examples below, multiple types of undulations have been developed that result in membrane bistability and enable modulation of the bistable switch temperature, e.g., through the thickness of membrane. The membrane is bistable only in its portion suspended over the cavity. The membrane under the electrical contacts is affixed to the buried oxide and is not bistable in these areas.

[0047] In the embodiments, the membrane consists of three layers. The top layer is aluminium, the middle layer is PVDF, while the bottom layer is the silicon layer.

[0048] In a first embodiment, the membrane has a concave shape and has additional bulges on both sides of the membrane, as shown in Fig. 3(a). The bistable membrane has a length of 1 mm and a thickness of 5 pm.

[0049] In a second embodiment, the membrane has the shape as shown in Fig. 4(a). In this embodiment, the bistable membrane has a length of 1 mm and a thickness of 15 pm.

[0050] In a third embodiment, the membrane has the shape as shown in Fig. 5(a). In this embodiment, the bistable membrane has a length of 1 mm and a thickness of 30 pm. In other embodiments, the membrane has a concave shape with additional concavities on both sides. The bistable membrane has a length of 20 pm and consists of three layers. The top layer with 15 nm thickness, is aluminium; the middle layer is PVDF with 100 nm thickness, while the bottom layer is the silicon layer with 20 nm thickness.

[0051] In alternative embodiments, the membrane has a concave shape with two additional bulges on both sides of the membrane.

[0052] In yet other embodiments, a concave membrane is employed, with an arc size of 25% of the total length of the membrane, while the membrane has a length of 500 pm and a thickness of 2 pm.

[0053] Membrane Deformation (Membrane Undulation)

[0054] Membrane deformation in the context of energy generation can take the convex or the concave form, depending on temperature conditions. Undulation is an essential feature for achieving membrane bistability in response to temperature changes, which in turn is indispensable for obtaining measurable electrical responses from the piezoelectric layer.

[0055] The bistable membrane (1) can be made of silicon or metal, wherein a silicon layer is the preferred variant in the present invention, and as such is illustrated in the figures.

[0056] In the case of the silicon SOI layer membrane, its undulation is obtained using SiN stressors, which take the form of etched strips disposed directly on the SOI layer. Depending on the method of deposition and annealing of SiN stressors, they can exhibit strong internal tensile or compressive stresses (a phenomenon well-known in the art) that are transferred to the silicon membrane, causing it to undulate. As demonstrated in M. Haras, J.-F. Robillard, T. Skotnicki, and E. Dubois, “Design and fabrication of nanometer measurement platform for better understanding of silicon mechanical properties, ’’ Journal of Applied Physics, vol. 134, no. 2, p. 024305, Jul. 2023, doi: 10.1063 / 5.0152192, silicon with a thickness of a few tens of nanometers can elongate by 8% of its initial length in this way, whereas H. Zhang, J. Tersoff, S. Xu, et al., in “Approaching the ideal elastic strain limit in silicon nanowires, ” Science Advances, vol. 2, no. 8, p. el501382, Aug. 2016, doi: 10.1126 / sciadv.1501382 have reported elongation of even 14.5%.

[0057] Various cross-sections and proportions of the undulation are obtained through different combinations of tensile and compressive stressors applied to the silicon membrane. Fig. 6 shows an example of the undulation obtained using two tensile stressors and one compressive stressor. It should be noted that the membrane undulation only appears after it is released from contact with the buried oxide layer, and that the stressors remain on the SOI layer and in subsequent steps are coated with the piezoelectric (7) and metal (6) layers. The stressors are not depicted in the schematic illustrations of the structure in Figs. 1 and 2.

[0058] In the case of a metal membrane, its undulation is obtained by leveraging the natural shape of resist domes subjected to thermal resist flossing. This process, known as "resist flossing," is well-established in the art and is used in the production of micro-lenses for smartphone-integrated cameras. Fig. 7 shows the basic steps for obtaining the bistable membrane undulation. After applying the resist and etching it to form a mosaic of domes, the plate is annealed, causing the resist to flow outward and take the desired shape. The plate is then coated with a metal layer, and strips are etched going across the domes before the metal membranes are released by etching out the resist. The metal membrane option is not illustrated in the schematic figures (1) and (2) of the transducer structure.

[0059] The membrane (1) made in this manner, coated with the piezoelectric layer (7) and the metal electrode (6) exhibits bistable behaviour as a function of temperature, provided that at least one of these layers has a thermal expansion coefficient significantly greater than that of the other layers. When such a layer expands due to temperature, it forces the bistable switch of the entire membrane from the convex to the concave state, or vice versa. Upon returning to the initial temperature, the layer with the significantly higher thermal coefficient then strongly contracts, triggering the bistable membrane to switch back to its original position. Each bistable switch leads to sudden and intense bending stress in the piezoelectric layer, leading in turn to the generation of a strong electrical signal.

[0060] Description of System Construction

[0061] The object of the invention is an energy generation module comprising a temperature transducer, whose substrate is made of a substrate silicon layer (3), on which a buried oxide layer (2) (so called BOX) is disposed. The substrate silicon layer (3) serves as the mechanical and electrical base for other components.

[0062] Silicon is widely used in microelectronics due to its semiconductor properties, making it ideal for integrated circuits and MEMS structures. The buried oxide layer (2) provides electrical and mechanical insulation, which is crucial for protecting the system from external influence and preserving the structural integrity of sensitive electronic components.

[0063] The top of the module is the bistable silicon membrane (1), which is susceptible to deformation as a result of changes in temperature of the cavity surroundings. On the membrane (1), the piezoelectric layer (7) is disposed, on which the metal electrode (6) is disposed, and simultaneously, on the metal electrode (6), the first electrical contact (9) is disposed, and on the silicon membrane (1), the second electrical contact 10 is disposed.

[0064] The metal electrode (6) can be made of any metal known to a person skilled in the art; therefore, the type of metal does not have a significant impact on the module according to the invention. The electrical contacts (9) and (10) can be made from the same metal or a different material, which is appreciated by a person skilled in the art and also does not significantly affect the performance of the module according to the invention.

[0065] The module according to the invention comprises at least two cavities, the bottom of which is the substrate silicon layer (3), and the walls constitute the buried oxide layer (2), a clearance is present between the cavities, as shown in Fig. 2, connecting both cavities.

[0066] The metal electrode (6) and the heavily doped SOI layer (1), which serves as the second electrode, enable the conduction of electric current and are key in the process of generating electrical signals from the piezoelectric layer (7). Optionally, the SOI layer (1) may be coated with a thin metal layer before the piezoelectric layer (7) is applied thereon. This leads to a slight complication of the design but may have a positive effect on the conductivity of the lower electrode beneath the piezoelectric layer, especially if the doping of the SOI layer is insufficient.

[0067] The first and the second electrical contacts (9) and (10) allow electrical connection of the system components with external circuits, which is necessary for transferring the generated electrical energy. Preferably, the piezoelectric layer (7) is made of PVDF (polyvinylidene fluoride) or its copolymers, which also exhibit piezoelectric properties, moreover, they show flexibility, lightness, and good processing properties, particularly in flexible and bendable piezoelectric devices. However, the most important advantage of using PVDF is its thermal coefficient, which is more than 10 times higher than the thermal coefficient of most metals and silicon. Because of that, PVDF has two important functions in the operation of the module: 1) it facilitates bistable switches; 2) it functions as a piezoelectric material, generating a strong electrical signal with each bistable switch.

[0068] Besides to the PVDF, other embodiments used:

[0069] - ZnO, which exhibits distinct piezoelectric properties, is chemically and thermally stable, which is important for maintaining piezoelectric properties in various environmental and temperature conditions, can be easily integrated with existing microfabrication technologies, which is crucial in the production of miniature piezoelectric devices. Furthermore, it is relatively easy to obtain and inexpensive, making it an attractive choice from a production cost perspective. - PZT (lead zirconate titanate), which has exceptionally strong piezoelectric properties,

[0070] - Barium titanate (BaTiCh), a ceramic material with good piezoelectric properties,

[0071] - Lithium niobate (LiNbCh) or quartz silicate, which are characterized by high strength and thermal stability.

[0072] - other materials that also exhibit piezoelectric properties, ensuring an analogous effect in the operation of the module according to the invention.

[0073] The membrane consisting of the silicon, the piezoelectric material, and the metal layers is designed to be sensitive to temperature changes. When the temperature increases or decreases, the membrane first accumulates elastic energy in the form of internal stress until it finally undergoes a rapid deformation - it deforms inward or outward. This rapid switch of the shape of the membrane is key to the functioning of the entire device.

[0074] The piezoelectric layer disposed on the silicon membrane reacts to the deformation of the membrane. The piezoelectric materials generate an internal electric field under mechanical deformation, which attracts electrons through the external circuit, thus restoring the electroneutrality of the sample.

[0075] The process is cyclic - temperature changes in the environment of the module may repeat, causing regular deformation and return of the membrane (1) to its original shape, which leads to cyclic generation of electrical energy.

[0076] The silicon membrane (1) is made using the SOI technology, which offers a range of technological benefits, particularly in processes such as etching the gap. The SOI technology ensures high precision and control over production processes. By using the insulating layer (BOX) between the silicon layers, it is possible to precisely define the thickness and properties of the silicon membrane (precise shaping of elements). Thanks to the SOI technology, the etching process of the gap in the buried oxide layer (BOX) can be accurately controlled and stopped at the substrate silicon layer. The substrate silicon, being part of the SOI structure, serves as a natural barrier stopping the etching process. This allows for precise dimensions and shapes of the silicon structure without the risk of damaging it. The SOI technology enables high precision and reproducibility in the production of components, which is crucial in precise applications in advanced microelectronics. Additionally, the electrical properties of the silicon membrane can be modified by doping.

[0077] The heavily doped silicon membrane (1) has modified electrical properties, allowing for precise control of electrical conductivity, where the membrane is used to generate electrical signals and functions as the conducting electrode. For effective energy harvesting from the piezoelectric signal, a fundamental feature of the membrane is its bistability, i.e., the build-up of internal stress within the membrane followed by a sudden switch from the concave to the convex state, or vice versa.

[0078] In an alternative embodiment, the membrane may also be made of metal, such as aluminium, titanium, tungsten, copper, or other good conductors, e.g., TiN (titanium nitride), TaN (tantalum nitride), etc., which would ensure an analogous effect in the operation of the module according to the invention.

[0079] The magnitude of arching refers to the shape that arches outward or inward. It is the difference in height between the edge and the central point of the membrane.

[0080] The thickness of the membrane refers to the sum of thickness of all layers constituting the membrane, i.e., the SOI layer (1) the piezoelectric layer (7), and the electrode layer (6).

[0081] The module according to the invention, in various embodiments, was subjected to testing, wherein the temperature applied to its surface varied within the range of 16-1000°C. The magnitude of arching (initial inward bending of the membrane into the module) was approximately 40 pm, as shown in Figs. 3, 4, and 5.

[0082] Figs. 3(c), 4(c), and 5(c) further show the results of COMSOL simulations, confirming the presence of an element activated at a specific temperature, causing a simultaneous rapid increase in displacement and generation of output voltage. The simulations provided pertain to a scenario wherein the piezoelectric layer is made of PVDF, which has a thermal expansion coefficient 10 times greater than that of the other layers, i.e., (1) and (6). In alternative embodiments, utilizing other piezoelectric materials, this coefficient was 2 or higher.

[0083] Application of the Invention

[0084] The transducer of temperature changes into electricity according to the invention may be particularly useful for applications associated with powering electronic systems with particularly low power (LP, low power) consumption. In practice, these are most often integrated circuits made using the VLSI (Very -Large-Scale of Integration) technology. Due to significant advancements in the degree of integration, based on the so-called Moore's Laws, today's LP VLSI circuits can perform 1 million logical operations per second (MIPS - million instructions per second) using up just 2.4 pj, in other words using the power of 2.4 pj / s. Because of these achievements, loT network nodes are now being developed that measure a particular physical parameter (e.g., temperature, pressure, CO2 concentration, etc.), analyse the acquired data using an integrated microprocessor, and transmit the results of the analysis via an integrated radio transmitter, consuming no more than 90 gJ of energy for the entire operation cycle. Moreover, loT sensor networks do not operate continuously; on the contrary, they perform such a measurement-analysis-radio transmission cycle every few seconds, minutes, hours, or even once every few days, depending on the application. For these reasons, the invention appears to be particularly suitable for powering loT network nodes.

[0085] Reference Signs List

[0086] 1 - Heavily doped silicon membrane also serving as the positive electrode 2 - BOX (buried oxide)

[0087] 4 - Substrate silicon of the SOI plate

[0088] 5 - Cavity

[0089] 6 - Metal electrode

[0090] 7 - Piezoelectric layer, e.g., PVDF 9 - First electrical contact

[0091] 10 - Second electrical contact

Claims

Claims1. An energy generation module comprising a transducer of temperature changes into electricity, characterized in that it comprises a substrate, which constitutes a substrate silicon layer (3), coated with a buried oxide layer (2) with etched areas forming cavities, and on the buried oxide layer (2) rests a membrane (1), which is supported at two opposite ends on the buried oxide (2), forming a bridge over the etched regions of the buried oxide (2), simultaneously, the membrane (1) has an undulated shape at its suspended (bridgeforming) part over the area with the etched buried oxide (2), and this part is susceptible to deformation due to change of temperature over time, and on the bistable membrane (1) a piezoelectric layer (7) is disposed, on which a metal electrode (6) is disposed, and simultaneously, on the metal electrode (6) a first electrical contact (9) is disposed, furthermore, the module comprises cavities (5a) and (5b) in the buried oxide layer (2), which are connected with each other by a tunnel located under a bistable part of the membrane (1), such that the bottom of the tunnel constitutes the substrate silicon layer (3), whereas the ceiling of the tunnel constitutes the bistable membrane (1), as well as a cavity (5c), in which a second electrical contact (10) is disposed on the membrane (1), simultaneously, the difference in the coefficient of thermal expansion between the bistable membrane layer (1), the metal electrode layer (6), and the piezoelectric layer (7) is at least twofold.

2. The generation module according to claim 1, characterized in that the bistable membrane (1) is a silicon membrane.

3. The generation module according to claim 2, characterized in that the bistable membrane (1) is made of a heavily doped silicon layer using the SOI technology.

4. The generation module according to claim 3, characterized in that the bistable silicon membrane (1) is coated with a thin metal layer to reduce the series resistance of the silicon layer.

5. The generation module according to claim 1, characterized in that the bistable membrane (1) is made of a metal selected from the group including aluminium, titanium, tungsten, copper, or a highly conductive material selected from the group including TiN (titanium nitride) and TaN (tantalum nitride).

6. The generation module according to any of claims 1-5, characterized in that the bistable membrane (1) has a length ranging from 20 gm to 20 mm, preferably 1 mm.

7. The generation module according to claim 1, characterized in that the piezoelectric layer (7) is made of a material selected from the group including ZnO, PZT (lead zirconate titanate), PVDF (polyvinylidene fluoride) and its copolymers, BaTiCh, LiNbCh, quartz silicate, or aluminium oxide.

8. The generation module according to claim 7, characterized in that the piezoelectric layer (7) is made of PVDF.

9. The generation module according to any of claims 1 or 7-8, characterized in that the piezoelectric layer (7) thickness is in the range of 10 nm to 1 mm.

10. The generation module according to claim 1, characterized in that the metal electrode (6) is made of aluminium.

11. The generation module according to claim 1 or 10, characterized in that a metal electrode (6) thickness is within the range of 15 nm to 1 mm.

12. The generation module according to any of claims 1-11, characterized in that the difference in the thermal expansion coefficients of the bistable membrane layer (1), the metal electrode layer (6), and the piezoelectric layer (7) is tenfold.

13. A set of modules as defined in claims 1-12 connected in series or in parallel.

14. Use of the set of modules according to claim 13 for powering loT network nodes.

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