CN108540046A - Integrated nano energy getter and preparation method in self energizing wireless sensing node - Google Patents

Abstract

The substrate of integrated nano energy getter and preparation method in the self energizing wireless sensing node of the present invention, device is N-type silicon chip, and being made on photronic light-receiving surface has suede structure, the first silicon nitride film and back of the body electric field structure；The monocrystalline silicon thin film of one layer of extension is covered on superlattice structure, is partly P-doped zone domain, is partly n-type doping region；It deposited layer of silicon dioxide layer passivation layer on monocrystalline silicon thin film, and a series of electrode contact hole opened in specific region, be connected with photronic base electrode and transmitting region electrode；The second silicon nitride film is separated between thermoelectric generator and photocell, critical piece thermoelectric pile is to be connected in series by being permitted polysilicon nanowire thermocouple, while having made multiple thermoelectric pile output electrodes；In the top of thermoelectric pile, the cavity structure produced is discharged by sacrificial layer, the top of cavity is metallic plate.

Description

Integrated nano energy harvester and preparation method in self-powered wireless sensor node

technical field

The invention provides an integrated nanometer energy obtainer in a self-powered wireless sensor node and a preparation method thereof, belonging to the technical field of micro-electro-mechanical systems (MEMS).

Background technique

With the rapid development of Internet of Things technology, more and more electronic devices will be connected to the network for data exchange, including various wireless sensor nodes, which can be used for environmental and building detection, animal tracking and control, process detection , national security and health applications, and more. By optimizing the circuit structure and adjusting the working mode of the transceiver components, the power consumption of the transceiver components can be controlled at the microwatt level. This low-power wireless network node can be directly powered by energy harvesting, avoiding the need for regular battery replacement. disadvantages. Among many energy harvesting methods, solid-state conversion devices can be used for light energy harvesting and thermal energy harvesting. There are no moving parts, high reliability, long service life, no maintenance, and no noise during operation. With the development of material science, the emergence of nanomaterials has opened up a new direction for thermoelectric and photoelectric research. In places with sufficient heat or light, thermoelectric energy harvesters and photoelectric energy harvesters based on nanomaterials and processes are wireless networks. Ideal power source for sensor nodes.

Contents of the invention

Technical problem: the object of the present invention is to provide a kind of self-powered wireless sensing node integrated nano-energy harvester and preparation method, photovoltaic cell and thermoelectric generator respectively adopt superlattice and polysilicon nanowire structure, in order to improve output power , and integrated on the same substrate, it can simultaneously acquire thermal energy and light energy in the environment. In a complex surrounding environment, the two acquisition methods can complement each other and provide synergistic power supply.

Technical solution: In order to solve the above technical problems, the present invention proposes an integrated nanometer energy harvester in a self-powered wireless sensor node and a preparation method. Its structure mainly includes a photovoltaic cell and a thermoelectric generator. The two parts are fabricated on the same silicon substrate, realizing the monolithic integration of thermoelectricity and photovoltaics, and the electrodes of the photovoltaic cell and the thermoelectric generator are located on the same side of the silicon wafer, which is convenient for practical use. The package in the application uses silicon nitride film as the insulating structure of the two parts to avoid electrical short circuit.

The substrate of the photovoltaic cell is an N-type silicon wafer with a long carrier life, and the light-receiving surface adopts a textured inverted pyramid textured structure, which is used to reduce the reflection of incident light; a layer of specific thickness is coated on the textured structure The anti-reflection silicon nitride film uses hydrogen passivation and fixed charge effect to reduce the bulk recombination and surface recombination of the battery; a N-N+ high-low junction is fabricated by ion implantation method, also known as the back electric field structure. In order to reduce surface recombination; amorphous silicon and silicon carbide nano-films are alternately arranged to form a superlattice structure, and a layer of epitaxial single-crystal silicon film is covered on the top of the superlattice structure, part of which is a P-type doped region, used as a photovoltaic cell Part of the emitter area is an N-type doped area, which is used to form an ohmic contact with the base electrode; the single crystal silicon film is covered with a passivation layer of silicon dioxide layer, and an electrode contact hole is opened to reduce the upper surface The surface composite, the interdigitated photocell electrodes include the base electrode and the emitter electrode. Compared with the traditional photocell structure, the electrode width on the upper surface is very large. On the one hand, it reduces the back reflection of the battery, and on the other hand, it reduces The parasitic resistance is beneficial to improve the output performance.

The thermoelectric generator is mainly composed of a horizontally placed thermopile and a heat-dissipating metal plate; the thermopile is composed of many thermocouples in series, and each thermocouple is composed of an N-type polysilicon nanowire thermocouple arm and a P-type polysilicon nanowire Composed of thermocouple arms, the thermocouple arms contain multiple columns of polysilicon nanowires, and nanowire support structures are used as connections between different columns to improve the stability and reliability of the structure; gold (Au) is used between the two semiconductor arms as thermoelectric Stack interconnected metals, because the heat is transferred from the hot end of the thermopile to the cold end, so the thermocouples are connected in parallel in terms of heat transfer and in series electrically; in order to facilitate testing and avoid local deviations from causing failure of the entire device, thermoelectric generators are made Multiple output electrodes are formed; above the thermopile, the cavity structure produced by releasing the sacrificial layer further enhances the thermal isolation between the hot and cold ends; the cold end of the thermoelectric generator is effectively realized by a metal plate It improves heat dissipation and increases the thermal coupling between the thermopile and the surrounding environment. The material of the metal plate is aluminum (Al), and there is a silicon nitride film between the thermopile and the thermopile to achieve insulation. Since the heat flow path is perpendicular to the chip surface, it is convenient for the device to be used in the application. in the package.

The working principle of the photovoltaic cell is as follows: when photons with appropriate energy are incident on the PN junction of the photovoltaic cell, the photons interact with the semiconductor material to generate electrons and holes. Under the action of the electric field in the PN junction region, the electrons diffuse to the N-type semiconductor and the holes Holes diffuse to the P-type semiconductor and gather in the two electrode parts respectively, generating a certain potential difference and simultaneously output power; when the electrode outputs power, in addition to the photo-generated current, due to the output voltage, there is also a junction "dark current" opposite to the photo-generated current. , the current output to the load is actually the difference between the photogenerated current and the dark current.

The working principle of the thermoelectric generator is as follows: when a certain temperature difference is applied to the hot and cold ends of the generator, heat will be injected from the hot end, after passing through the thermopile, and finally discharged from the cold end, and form a certain temperature distribution on the thermoelectric generator ;Because there is a certain thermal resistance of the thermopile, there will be a corresponding temperature difference between the hot and cold junctions of the thermopile. Based on the Seebeck effect, the two ends of the thermopile will output a potential proportional to the temperature difference. After connecting the load, it can be realized power output.

In practical applications, the light-receiving surface of the photovoltaic cell faces upwards to receive light from the environment, and the other surface of the covered metal plate is attached to the radiator; after the energy obtained by the photovoltaic cell and the thermoelectric generator passes through the DC-DC conversion module, It is stored in the battery and supplies power to various wireless sensor nodes arranged around the power amplifier.

Beneficial effect: the present invention has the following advantages compared with the existing energy harvester:

1. The present invention adopts mature CMOS technology and MEMS technology, which has the advantages of small size, low cost, batch manufacturing, and the ability to realize monolithic integration with microelectronic circuits;

2. The monolithic integration of thermoelectric and photoelectric energy harvesting methods has been realized. In complex surrounding environments, the two harvesting methods can complement each other and provide collaborative power supply;

3. The photovoltaic cell adopts a full back electrode structure, which has the advantages of no shading loss, low electrode series resistance and easy device interconnection compared with the traditional photovoltaic cell structure;

4. The nanometer size effect of the superlattice makes the photovoltaic cell have excellent photosensitivity, photoelectric characteristics, high conductivity, high light absorption coefficient and high optical band gap, and the photoconductivity has a small attenuation under light conditions, thereby improving the efficiency of the photovoltaic cell ;

5. The thermoelectric generator adopts a hybrid structure, that is, the heat flow path is perpendicular to the chip surface, and the current path is parallel to the chip surface. The heat flow path perpendicular to the chip surface simplifies the packaging of the device, and the thermopile located in the chip plane can be Manufactured by IC compatible technology, it has high integration density and large output voltage density;

6. The thermocouple of the thermoelectric generator uses polycrystalline silicon nanowires. Due to quantum confinement and phonon scattering effects, the thermal conductivity of polycrystalline silicon nanowires is much lower than that of traditional bulk materials, which improves the thermoelectric conversion efficiency of thermoelectric generators;

7. Photovoltaic cells and thermoelectric generators are solid-state energy converters with no moving parts, high reliability, long service life, no maintenance, and no noise during operation;

8. All electrodes of the integrated nanometer energy harvester are on the same plane, avoiding complicated electrical connections like via holes.

Description of drawings

Fig. 1 is the schematic diagram of the application of the integrated nano-energy harvester in the self-powered wireless sensor node of the present invention;

Fig. 2 is a schematic structural diagram of the polycrystalline silicon nanowire thermocouple arm of the integrated nano energy harvester in the self-powered wireless sensor node of the present invention;

Fig. 3 is a top view structural schematic diagram of an integrated nano-energy harvester in a self-powered wireless sensor node of the present invention;

Fig. 4 is a schematic diagram of a top view structure after the electrode of the thermoelectric generator of the present invention is prepared;

Fig. 5 is a top view structural schematic diagram after the preparation of the photovoltaic cell electrode of the present invention is completed;

Fig. 6 is a cross-sectional view of the device A-A' of the integrated nano-energy harvester in the self-powered wireless sensor node of the present invention.

The figure includes: a photovoltaic cell 1, a thermoelectric generator 2, a substrate 3, a textured structure 4, a back electric field structure 5, a first silicon nitride film 6, a superlattice structure 7, a single crystal silicon film 8, an N-type doped Impurity region 9, base electrode 10, emitter electrode 11, second silicon nitride film 12, N-type polysilicon nanowire thermocouple arm 13, P-type polysilicon nanowire thermocouple arm 14, thermopile interconnection metal 15, third Silicon nitride film 16, metal plate 17, silicon dioxide passivation layer 18, thermoelectric generator output electrode 19, polysilicon nanowire 20, nanowire support structure 21, light receiving surface 22, radiator 23, DC-DC conversion Module 24, battery 25, wireless sensor node 26.

Detailed ways

The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

Referring to Figures 1-6, the present invention proposes an integrated nanometer energy harvester in a self-powered wireless sensor node and a preparation method thereof. The structure mainly includes a photovoltaic cell 1 and a thermoelectric generator 2. The two parts are fabricated on the same silicon substrate 3, realizing the monolithic integration of thermoelectricity and photovoltaics, and the electrodes of the photovoltaic cell 1 and the thermoelectric generator 2 are located on the same silicon substrate. The side is convenient for packaging in practical applications, and the second silicon nitride film 12 is used as the insulating structure of the two parts to avoid electrical short circuit.

The substrate 3 of the photovoltaic cell is an N-type silicon wafer with a long carrier life, and the light-receiving surface 22 adopts a textured inverted pyramid textured structure 4, which is used to reduce the reflection of incident light; the textured structure 4 is coated with A layer of anti-reflective first silicon nitride film 6 with a specific thickness uses hydrogen passivation and fixed charge effect to reduce the bulk recombination and surface recombination of the battery; an N-N+ high-low junction is fabricated on the lower surface by ion implantation, and Known as the back electric field structure 5, it is used to reduce surface recombination; on the upper surface of the battery, amorphous silicon and silicon carbide nano-films are alternately arranged to form a superlattice structure 7, each layer thickness is 2-10nm, the superlattice The nano-size effect makes the photovoltaic cell 1 have excellent photosensitivity, photoelectric characteristics, high conductivity, high light absorption coefficient and high optical band gap, and the photoconductivity has a small attenuation under light conditions, thereby improving the conversion efficiency of the photovoltaic cell 1; The top of the lattice structure 7 is covered with a layer of epitaxial single crystal silicon thin film 8, part of which is a P-type doped region, which is used as the emission region of the photovoltaic cell, and part of which is an N-type doped region 9, which is used to form an ohmic region with the base electrode 10. Contact, the monocrystalline silicon film 8 is covered with a layer of silicon dioxide passivation layer 18, and a series of electrode contact holes are opened to reduce the surface recombination of the upper surface. The interdigitated photocell electrodes include base electrodes 10 and Compared with the traditional photovoltaic cell structure, the emitter electrode 11 has a larger electrode width on the upper surface. On the one hand, it reduces the back reflection of the battery, and on the other hand, it reduces the parasitic resistance of the battery, which is beneficial to improve the output performance.

The thermoelectric generator 2 is mainly composed of a thermopile placed horizontally and a heat-dissipating metal plate 17; the thermopile is composed of many thermocouples connected in series, and each thermocouple is composed of an N-type polysilicon nanowire thermocouple arm 13 and a P-type polysilicon The nanowire thermocouple arm 14 is composed of multiple rows of polysilicon nanowires 20 on the thermocouple arm. The width of the nanowires is 1-100 nm, and the length is 1-10 μm. The distance between the polysilicon nanowires 20 in the same row is 1-100 nm. The nanowire support structure 21 is used as a connection between different columns to improve the stability and reliability of the structure; due to quantum confinement and phonon scattering effects, the thermal conductivity of polycrystalline silicon nanowires 20 is much lower than that of traditional bulk materials, which improves the thermoelectric performance. The thermoelectric conversion efficiency of the generator 2; Au is used as the thermopile interconnection metal 15 between the two semiconductor arms, because the heat is transferred from the hot end of the thermopile to the cold end, so the thermocouples are connected in parallel in heat transfer and connected in series electrically ; In order to facilitate testing and avoid failure of the entire device caused by local deviations, the thermoelectric generator has produced a plurality of thermopile output electrodes 19; above the thermopile, the cavity structure made by releasing the sacrificial layer further enhances the thermal stability. Thermal isolation between the two ends; the cold end of the thermoelectric generator effectively realizes heat dissipation through a metal plate 17, which increases the thermal coupling between the thermopile and the surrounding environment. The material of the metal plate 17 is Al, and the distance between the thermopile and the thermopile is There is a third silicon nitride film 16 to realize insulation; since the heat flow path is perpendicular to the chip surface, it is convenient to package the device in application.

The working principle of photovoltaic cell 1 is as follows: when photons with appropriate energy are incident on the PN junction of the photovoltaic cell, the photons interact with the semiconductor material to generate electrons and holes. Under the action of the electric field in the PN junction region, the electrons diffuse to the N-type semiconductor, Holes diffuse to the P-type semiconductor and gather in the two electrode parts respectively to generate a certain potential difference and output power at the same time. When the electrode outputs power, in addition to the photo-generated current, due to the output voltage, there is also a junction "dark current" opposite to the photo-generated current, and the current output to the load is actually the difference between the photo-generated current and the dark current.

The working principle of thermoelectric generator 2 is as follows: when a certain temperature difference is applied between the hot and cold ends of the generator, heat will be injected from the hot end, after passing through the thermopile, and finally discharged from the cold end, and form a certain temperature on the thermoelectric generator. distributed. Due to the certain thermal resistance of the thermopile, there will be a corresponding temperature difference between the hot and cold junctions of the thermopile. Based on the Seebeck effect, the two ends of the thermopile will output a potential proportional to the temperature difference, and the power output can be realized after connecting the load. .

In practical application, as shown in FIG. 1 , the light-receiving surface 22 of the photovoltaic cell 1 faces upwards to receive light in the environment, and heat is generated due to light. On the radiator 23, as the cold end of the device; the energy obtained by the photovoltaic cell 1 and the thermoelectric generator 2 passes through the DC-DC conversion module 24, and is stored in the battery 25, which can be various devices arranged around the power amplifier. Power is supplied to the wireless sensor nodes 26 .

The preparation method of the integrated nano-energy harvester in the self-powered wireless sensor node of the present invention is as follows:

1) Select an N-type silicon wafer as the substrate 3, the doping concentration of phosphorus is 1×10 ¹⁵ cm ^-3 , and the resistivity is about 5Ωcm. Before fabrication, perform double-sided polishing and soak in hydrofluoric acid solution to remove metal impurities such as particles;

2) On the substrate, a plasma-enhanced chemical vapor deposition (PECDV) process is used to fabricate an amorphous silicon silicon carbide nano-superlattice structure 7, and the amorphous silicon and silicon carbide films are arranged alternately, with a thickness of 2nm and 4nm respectively;

3) Epitaxially layer a single crystal silicon thin film 8 on the upper surface of the silicon wafer, perform boron ion diffusion doping with a doping concentration of 1×10 ²⁰ cm ^-3 , and form a P+ region as a photoelectric PN junction emitter;

4) A layer of silicon nitride is deposited by PECVD with a thickness of about 200nm, and formed by photolithography. Here, buffered hydrofluoric acid is used to remove silicon nitride in a specific area, as a window for subsequent phosphorus ion implantation;

5) Phosphorus ion implantation and annealing, using hydrofluoric acid to remove silicon nitride in the remaining area;

6) Deposit a layer of 100nm silicon dioxide by PECVD process and photolithographically form it as the silicon dioxide passivation layer 18, and expose the electrode contact area;

7) Fabricate a textured structure 4 on the back of the N-type silicon wafer, then perform P ion implantation to form a back electric field structure 5, and then use PECVD to deposit the first silicon nitride film 6 as an optical anti-reflection layer;

8) Evaporate a 2 μm thick aluminum layer and perform photolithography to form the interdigital electrodes of the photovoltaic cell, including the base electrode 10 and the emitter electrode 11;

9) Depositing a second silicon nitride film 12 as an electrical insulating layer by using a PECVD process;

10) A polysilicon film with a thickness of 1 μm is grown by a low-pressure chemical vapor deposition (LPCDV) process;

11) Forming polysilicon nanowires 20 by electron beam lithography or extreme ultraviolet lithography;

12) Perform N-type phosphorus ion doping and P-type boron ion doping on the corresponding regions of the polysilicon nanowire 20 to form N-type polysilicon nanowire thermocouple arms 13 and P-type polysilicon nanowire thermocouple arms 14;

13) Evaporate a gold layer with a thickness of 0.2 μm, and form it by lift-off method to form thermopile interconnect metal 15 and thermopile output electrode 19;

14) A layer of silicon nitride film is grown by PECVD process, with a thickness of 0.1 μm, as a dielectric insulating layer and a protective layer;

15) Spin-coat a layer of polyimide with a thickness of 3 μm, and photolithographically form it as a sacrificial layer;

16) electroplating a layer of metal aluminum with a thickness of 1 μm, and photolithographically forming it as a heat dissipation metal plate 17 of the device;

17) After ultrasonic cleaning, place the silicon wafer in acetone for 10 minutes, then immediately put it in ethanol for 10 minutes to release the polyimide sacrificial layer, and finally rinse with water and shake dry.

The criteria for distinguishing whether it is the structure are as follows:

In the self-powered wireless sensor node of the present invention, the substrate 3 of the integrated nano-energy harvester is an N-type silicon chip, and the light-receiving surface 22 of the photocell is made with a textured structure 4, a first silicon nitride film 6 and a back electric field structure 5 , the superlattice structure 7 is covered with a layer of epitaxial monocrystalline silicon film 8, part of which is a P-type doped region, and part of which is an N-type doped region 9. The nanometer size effect of the superlattice makes the photovoltaic cell have excellent photosensitivity , photoelectric properties, high electrical conductivity, high light absorption coefficient and high optical band gap, and the photoconductive attenuation is small under light conditions, thereby improving the efficiency of photovoltaic cells; a layer of silicon dioxide layer is deposited on the single crystal silicon film 8 passivation layer 18, and opened a series of electrode contact holes, connected with the base electrode 10 and the emitter electrode 11 of the photovoltaic cell; the second silicon nitride film 12 is separated between the thermoelectric generator 2 and the photovoltaic cell 1, and the thermoelectric The main part thermopile of generator 2 is formed by many thermocouples connected in series, and each thermocouple is made of N-type polysilicon nanowire thermocouple arm 13 and P-type polysilicon nanowire thermocouple arm 14. The thermocouple arm contains Multiple rows of polysilicon nanowires 20, with nanowire support structures 21 as connections between different rows, improve the stability and reliability of the structure. The thermocouple of the thermoelectric generator uses polysilicon nanowires, due to quantum confinement and phonon scattering effects, The thermal conductivity of polycrystalline silicon nanowires is much lower than that of traditional bulk materials, which improves the thermoelectric conversion efficiency of thermoelectric generators; Au is used as the thermopile interconnection metal15 between the two semiconductor arms, and multiple thermopile output electrodes19 are produced at the same time ; above the thermopile, release the cavity structure produced by the sacrificial layer, the top of the cavity is a metal plate 17, and the third silicon nitride film 16 is separated from the thermopile; in the process, the device adopts mature CMOS and MEMS is prepared in a compatible process, small in size, low in cost, capable of mass production, and capable of monolithic integration with microelectronic circuits.

A structure that satisfies the above conditions is regarded as the integrated nanometer energy harvester and its preparation method in the self-powered wireless sensor node of the present invention.

Claims (3)

1. integrated nano energy getter and preparation method in a kind of self energizing wireless sensing node, it is characterized in that：Device by (2) two parts of photocell (1) and thermoelectric generator being made on same substrate (3) are constituted, and centre is separated with the second nitridation Silicon thin film (12), making on the light-receiving surface (22) of substrate (3) has suede structure (4), the first silicon nitride film (6) and carries on the back electric field knot Structure (5)；The monocrystalline silicon thin film (8) of one layer of extension is covered above superlattice structure (7), is partly P-doped zone domain, portion It is divided into n-type doping region (9), layer of silicon dioxide layer passivation layer (18) is deposited on monocrystalline silicon thin film (8), silicon dioxide layer is blunt The electrode contact hole changed on layer (18) is connected with photronic base electrode (10) and transmitting region electrode (11)；Thermoelectric generator (2) critical piece is thermoelectric pile, and thermoelectric pile one end is located above base electrode (10) and transmitting region electrode (11), other end position In the gap location of base electrode (10) and transmitting region electrode (11), it is connected in series by many thermocouples, thermoelectric pile surrounding makes Multiple thermoelectric pile output electrodes (19)；In the top of thermoelectric pile, the cavity structure produced is discharged by sacrificial layer, cavity it is upper Side is metallic plate (17), and third silicon nitride film (16) is separated between thermoelectric pile；Nano super-lattice structured (7) by non-crystalline silicon and Carborundum films are alternately arranged, and per layer thickness in 1-10nm, the nanometer size effect of nano super-lattice structured (7) makes photoelectricity Pond possesses excellent light sensitivity, photoelectric characteristic, high conductivity, the high absorption coefficient of light and high optical band gap, and photoconduction is in illumination Under the conditions of decay it is smaller, to improve the efficiency of photocell (1)；The thermoelectric pile of thermoelectric generator (2) is by N-type polycrystalline silicon Nano wire thermocouple arm (13) and p-type polysilicon nano wire thermocouple arm (14) are constituted, and include multiple row polysilicon on thermocouple arm Nano wire (20), the width of nano wire are 1-100nm, and length is 1-10 μm, between same row polysilicon nanowire (20) between Away from for 1-100nm, using nanometer wire-braced structures (21) as connection between different lines；Because quantum confinement and phon scattering are imitated It answers, the thermal conductivity of polysilicon nanowire (20) is far below conventional bulk, improves the conversion efficiency of thermoelectric of thermoelectric generator.

2. integrated nano energy getter and preparation side in a kind of self energizing wireless sensing node according to claim 1 Method, it is characterized in that：Base electrode (10) and transmitting region electrode (11) are interlaced, and interdigitated arrangement is presented.

3. integrated nano energy getter and preparation side in a kind of self energizing wireless sensing node according to claim 1 Method, it is characterized in that：The light-receiving surface (22) of photocell (1) is for the light in environment of accepting, metallic plate (17) in practical applications It is affixed on radiator (23)；After the energy that photocell (1) and thermoelectric generator (2) obtain is by DC-DC conversion modules (24), It is stored in battery (25), can be various wireless sensing nodes (26) power supply for being arranged in power amplifier periphery.