Field of Invention

The present invention relates to an energy harvesting system and more particularly to a monolithically integrated multi- energy harvesting system and energy storage device and methods thereof.

Background of the Invention

Energy harvesting is defined as a process by which energy is derived from external sources such as solar energy, thermal energy, wind energy etc., captured and stored for small wireless autonomous devices. Energy harvesters provide power to low-energy electronics . The input fuel to some large- scale energy generation costs money (oil, coal, etc.) whereas the energy source for energy harvesters is present as an ambient background and is, therefore, free. Essentially, energy harvesting devices/systems convert this ambient background energy into electrical energy to power low energy devices. Such devices hold much promise for renewable energy to power up small and low power devices such as health monitoring and wireless system network applications. Such devices (health monitoring devices) require continuous data monitoring with a high frequencies of data communication which explains a need to have a continuous power source to power such devices without any interruption.

The energy from ambient sources may be stored in number of energy storage devices such as battery, capacitor, super- capacitors etc. Capacitors are mostly used in applications where high energy spikes are required for operation. But most of the energy harvesting devices has their energy storage units/modules located out of the main unit/system which makes it inefficiently connected to maximize harvesting efficiency.

Figure 1 illustrates a generic energy harvesting system. The generic harvesting system includes energy harvesting cell(s) (102), an electronic circuitry (104), an energy storage unit (106) and a load (108) . One challenge encountered while μsing current energy harvesting devices which have capacitors or super capacitors are energy storage units is that their capacity is limitation. For example, the capacity for batteries such as AA battery is about 1500-2500 mAhr while a super-capacitor with IF is roughly equals to ImAhr capacity only. This implied that an approximately 2000F super-capacitor may be needed to reach the same capacity of AA battery. This scaling-up operation may need a bigger size of super-capacitor design which will increase charging time to charge such super-capacitor in current systems. Further, the number of super-capacitor required may also increase and will depend on the application. While the number of energy harvesting cells depends on the super-capacitors used and whether they are connected in series or parallel. Further, the energy harvesting cells, electronic circuits and the energy storage need to be connected efficiently to maximize harvesting efficiency. Moreover, current ambient energy harvesting systems /devices are not capable of driving energy from multiple sources in parallel for their working and therefore the choice of using ambient energy remains very limited e.g., either solar energy harvesting or chemical energy harvesting etc.

Accordingly, there is a need for an energy harvesting system that not only continuously operates during periods of insufficient ambient energy but is also easily scalable and viable in terms of charging duration to scale up for high energy requirements and is capable of deriving energy from multiple sources in parallel. Summary of Invention

In view of foregoing, embodiments herein provide monolithically integrated multi energy harvesting syst with embedded storage.

In an aspect, an integrated multi energy harvesting and energy storage system is provided. The system includes a number of energy harvesting units (202) fabricated on a substrate, and the energy harvesting unit extracts energy from a number of ambient energy sources; and at least one energy storage unit (204) fabricated on the substrate and the energy storage unit stores energy harvested by the energy harvesting units. The energy harvesting units and the energy storage unit are monolithically integrated by fabrication on the substrate platform.

The system further includes an electric circuit (206) on the substrate platform, and the electric circuit harvests, boosts and regulates energy harvested. The substrate is selected from silicon, ceramic, plastic, Teflon, polymer or glass. The electric circuit (206) connects plurality of the harvesting units in parallel or series. The harvesting units (202) extract energy from ambient solar energy or ambient chemical energy. In another aspect, a method of fabricating monolithically integrated multi energy harvesting and energy storage system is provided. The method includes deposition of an oxide layer (304) as an insulator on a substrate (302); deposition of a common conductor layer as a back contact layer (306) on top of the oxide layer (304) ; patterning the back contact layer (306) by removing unwanted area followed by removing of resist; deposition of a first electrode layer (308) after removing an unwanted area of the back contact layer (306) that leaves the first electrode layer (308) on a back contact of a first harvesting unit and an energy storage unit; deposition of an absorber layer (310 ) followed by removal of an unwanted area that leaves the absorber layer (310) on a back contact of a second harvesting unit; deposition of a window layer (312) followed by removal of an unwanted area that leaves the window layer (312) on top of the absorber layer (310) of the second harvesting unit; deposition of a polymer electrolyte (314) followed by removal of an unwanted area that leaves the polymer electrolyte (314) on top of the first electrode layer (308) of the first harvesting unit and the energy storage unit; deposition of a transparent conducting oxide (TCO) layer (316) followed by patterning and etching of unwanted area that leaves the TCO layer (316) on the window layer (312) of the second harvesting unit; deposition of a second electrode layer (318) followed by patterning and etching of an unwanted area that leaves the second electrode layer (318) on the polymer electrolyte (314) of the first energy- harvesting unit and the energy storage unit; deposition of an oxygen diffusion layer (320) on top of the second electrode layer (318) of the first energy harvesting unit; deposition of the top collecting layer (322), on the first energy harvesting unit, the second energy harvesting unit and the energy storage unit; deposition of an anti- reflective coating (ARC) layer (324) followed by removal of an unwanted area of the ARC layer (324) that leaves the ARC layer (324) on the TCO layer (316) of the second energy harvesting unit; and deposition of a non-conductive layer (326) to package the first and second energy harvesting units and the energy storage unit. The etching is selected from dry etching or wet etching.

The deposition is done by RF sputtering or ion beam formation and the oxide layer (304) is deposited on the substrate (302) by plasma enhanced vapour deposition technique. The first harvesting unit is chemical energy harvesting unit and the second harvesting unit is solar energy harvesting unit. Brief Description of the Drawings

Other objects, features, and advantages of the invention will be apparent from the following description when read with reference to the accompanying drawings . In the drawings, wherein like reference numerals denote corresponding parts throughout the several views :

Figure 1 illustrates a generic energy harvesting system;

Figure 2 is a top view of monolithically integrated system with multi energy harvesting and energy storage capabilities, according to an embodiment herein; Figure 3 is the cross view of monolithically integrated system with multi energy harvesting and energy storage capabilities, according to an embodiment herein; and

Figure 4 illustrates a flow chart of fabricating the monolithically integrated system with multi energy harvesting and energy storage capabilities, according to an embodiment herein. Detailed Description of the Preferred Embodiments

The present invention will now be described in detail with reference to the accompanying in drawings .

As stated above, there is a need for an energy harvesting system that not only continuously operates during periods of insufficient ambient energy but is also easily scalable and viable in terms of charging duration to scale up for high energy requirements and is capable of deriving energy from multiple sources in parallel.

The current embodiments provide a monolithically integrated multi energy harvesting and energy storage system to overcome limitations of the prior art. The system utilises multi energy harvesting i.e. it is not limited to harvesting only one type of ambient energy like solar energy or chemical energy rather other forms of ambient energy may also be utilised using the system. Further, the monolithically integrated system has embedded energy storage .

Figure 2 is a top view of monolithically integrated system with multi energy harvesting and energy storage capabilities, according to an embodiment herein. The top view includes multiple energy harvesting cells (202) , an energy storage unit (204) and an electronic circuit (206) . Multiple energy harvesting cells (202) enable use of multiple ambient energies by the system. Further, the energy storage system (204) is embedded within the ambient energy harvesting system which reduces charging time of the energy storage. Energy harvesting cells may be integrated in serial or parallel to increase an output current or voltage. The electronic circuit (206) is required to harvest, boost and regulate the harvested energy on a single platform or device. Energy storage is used to store the electrical energy harvested by the electronic circuit.

Figure 3 is the cross view of monolithically integrated system with multi energy harvesting and energy storage capabilities, according to an embodiment herein. The cross view includes a substrate layer (302), an oxide layer (304), a back contact layer (306) , a first electrode layer (308) , an absorber layer (310), a window layer (312), a polymer electrolyte (314) , a transparent conductive oxide layer (316) , a second electrode layer (318) , an oxygen diffusion layer (320), a top collecting layer (322) , an anti- reflective coating layer (324) and a non-conductive layer (326) . The substrate layer (302) is made up of commonly available substrates such as silicon etc. Further, the substrate layer (302) is coated with the oxide layer (304). The oxide layer (304) is further coated with the back contact layer (306). The energy storage unit includes the first electrode layer (308) coated above the back contact layer (306) with the polymer electrolyte (314) coating on the first electrode layer (308) . Further, the polymer electrolyte (308) is coated with the second electrode layer (318) further coated with the top collecting layer (322). The whole of the energy storage unit is embedded in the non- conductive layer (326) with top also coated with the same.

In one embodiment, only two energy harvesting units are included. Figure 2 includes two harvesting units designed for deriving energy from different energy sources. In the first energy harvesting unit, the back contact layer (306) is coated with the first electrode layer (308) which is further coated with the polymer electrolyte (314) . The polymer electrolyte (314) in this harvesting unit is further coated with the second electrode layer (318) . The second electrode layer has a coating of two different layers of the oxygen diffusion layer (320) and the top collecting layer (322) . In one embodiment, the first energy harvesting unit is ambient chemical energy harvesting unit. The second harvesting unit includes a coating of the absorber layer ( 310 ) on the back contact layer ( 3 06 ) . The absorber layer is coated with the window layer ( 312 ) which is further coated with the transparent conductive oxide layer ( 316 ) . The transparent conductive layer ( 316 ) is coated with two different layers of the anti-reflective coating layer ( 324 ) and the top collecting layer ( 322 ) on two portions of its surface. In one embodiment, the second harvesting unit is solar energy harvesting unit.

The monolithically integrated multi energy harvesting and energy storage system uses a common monolithic platform i.e. a single substrate for both energy harvesters and energy storage unit. Multiple energy harvesters on a single substrate enable extraction of energy from multiple ambient sources. The electronic circuit harvest, boost and regulate the harvested energy on same platform. In one embodiment, chemical energy harvester, solar energy harvester and other ambient energy harvester are used. In one embodiment, the monolithically integrated system has more than one energy storage units on same substrate.

Energy storage element embedded in the energy harvesting system will realize the continuous device operation by storing the energy harvested from the ambient energy harvesting cell. By using the multi energy harvesting with smaller energy harvesting cell size in a several separated group, make the system more robust and efficient to charge the energy storage.

Further, the apparatus of Figure 2 and Figure 3 may consist of several combinations of energy harvesting cells electronic circuits and energy storage components on a same substrate. The components may be fabricated on but not limited to silicon, ceramic, plastic, Teflon, polymer and glass only. The energy harvesting components and energy storage may share same manufacturing technique for the back contact layer (306) and top collecting layer (322) using. The back contact layer (306) and the top collecting layer (322) may be fabricated using a conductive material such as metal, alloy or metal alloy.

Figure 4 illustrates a flow chart of fabricating the monolithically integrated system with multi energy harvesting and energy storage capabilities, according to an embodiment herein. In step (402) , the oxide layer (304) as an insulator on a substrate (302) is formed. In one embodiment, plasma enhanced vapour deposition technique is used to deposit the oxide layer (304) on the substrate (302) . In step (404) , a common conductor layer as the back contact layer (306) on top of the oxide layer (304) is deposited. Methods such as RF sputtering or ion beam evaporation may be used to deposit the back contact layer (306) . In step (406) the back contact layer (306) is patterned with removing unwanted area by dry etching followed by removing of resist. In one embodiment, the lithography technique and dry etching of the unwanted area using mixed gas such as but not limited to chlorine and oxygen, to pattern the back contact layer (306) .

In step (408), the first electrode layer (308) is deposited, using RF sputtering or ion beam evaporation, with the unwanted area removed by dry etching the unwanted back contact layer (306), that leaves the first electrode layer (308) on a back contact of first energy harvesting unit and the energy storage unit. In one embodiment, the first electrode layer is aluminium.

In step (410) , the absorber layer (310) is deposited, either by RF sputtering or ion beam evaporation followed by removal of the unwanted area by dry etching that leaves the absorber layer (310) on a back contact of a second energy harvesting unit . In step (412), the window layer (312) is deposited by chemical vapour deposition technique followed by removal of the unwanted area by dry etching that leaves the window layer (312) on top of the absorber layer (310) of first harvesting unit.

In step (414) , polymer electrolyte (314) is deposited followed by removal of the unwanted area by etching that leaves the polymer electrolyte (314) on top of first electrode layer (308) of the first harvesting unit and storage unit.

In step (416) , the transparent conducting oxide (TCO) layer (316) is deposited, either by Physical Vapour Deposition or electron beam evaporation, followed by patterning and etching of the unwanted window layer (312), leaving the TCO layer (316) on the window layer (312) of the second harvesting unit. In step (418), the second electrode layer (318), such as but not limited to Nickel, is deposited, by RF sputtering followed by patterning and wet etching of the unwanted area using FeCl3 that leaves the second electrode layer (318) on polymer electrolyte (314) of the first energy harvesting unit and energy storage unit. In step (420) , the oxygen diffusion layer (320) , using mixture of paste such as but not limited to carbon, manganese and catalyst, is formed on top of the second electrode layer (318) of the first energy harvesting unit.

In step (422), the top collecting layer (322), such as but not limited to Silver is deposited on the first energy harvesting unit, the second energy harvesting unit and the energy storage unit.

In step (424), the anti-reflective coating (ARC) layer (324) is deposited followed by removal of the unwanted ARC layer (324) by etching that leaves the ARC layer (324) on the TCO layer (316) of the second energy harvesting unit. In step (426), the non-conductive layer (326), such as but not limited to epoxy, is formed to package for both the energy harvesting units and energy storage units.