NL2024940B1 - Crystalline semiconductor chip that can be curved in two directions - Google Patents

Abstract

The invention relates to a method for producing a chip that can be curved in two direction, the chip showing a periphery, the method comprising a step of providing a chip, the method characterized in that the method comprises a step of making through-slots (6, 7, 8, 9) in the chip. By dividing the chip (such as a photovoltaic cell or a logic chip) in number of connected flaps, a chip is formed with a high degree of flexibility that can be used using a small number of electrical connections.

Description

Crystalline semiconductor chip that can be curved in two directions Technical field of the invention.

[0001] The invention relates to a method for producing a crystalline semiconductor chip that can be curved in two direction, the chip showing a periphery, the method comprising a step of providing a chip Acknowledgement.

[0002] The project leading to this application has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No.

848620. Background of the invention.

[0003] In the context of this invention the phrase ‘chip’ includes ‘solar cell’, also known as ‘photovoltaic cell’ or ‘PV cell’. These phrases are used interchangeable.

[0004] Thin chips, such as certain types of crystalline silicon solar cells, can be curved. Curving the chip enables the chip to be attached to a curved transparent cover, as shown in, for example, US patent application US2019/0181283A1 to Toyota, further referred to as Toyota [-1-]. Toyota [-1-] describes how a sandwich of a flat back plate, a sealant (encapsulant), strings of interconnected solar cells, and finally another sealant (encapsulant) are heated and pressed together by a curved jig and a similarly curved transparent cover plate. The result is a curved solar panel comprising the transparent cover and bonded to that encapsulated solar cells.

[0005] A solar cell is mostly rectangular {although other forms such as hexagonal or octagonal are known). To achieve a high flexibility (to achieve small radius of curvature) such a cell has a thickness of, for example, 80 um. Although a smaller thickness would increase the flexibility, this results in an increase of transparency of the solar cell and thus a reduced efficiency.

[0008] Another example of curved chips is described in, for example, “Ultra-thin chips for high-performance flexible electronics”, Gupta, S et al. . npj Flex Electron 2, 8 (2018). hitps://doi.org/10.1038/841528-018-0021-5, further referred to as Gupta [-2-].

[0007] It is noted that bending a chip in only one direction results in much lower mechanical stress than when bending locally a chip in two directions. Therefore, a solar cell (a chip) can be bended, (flexed) in only one direction only, or, more accurate, it may not show local bending in two directions as happens in a saddle point or a dome, as otherwise the resultant stress may exceed the fracture limit, resulting in fracture of the chip.

[0008] It is further noted that a flexible chip must not be confused with a MEMS chip, in which a small (surface) part of a chip can be flexed with respect to the flat (non-flexible) bulk of the chip.

[0009] As known to the skilled artisan a solution for this problem is to divide the chip into a multitude of smaller chips, in which each chip can be seen as flat or curved in one direction, with a negligible curvature in another direction. A disadvantage of using a large number of solar cells or flexible chips is that the amount of interconnection raises as well.

Also, the positioning of the cells involves the positioning of a large number of cells or flexible chips. This results in more expensive and error prone solar panels or flexible electronic circuit.

Summary of the invention.

[0010] The invention intends to provide flexible chips with a larger surface area, more specifically solar cells to be used in conjunction with double curved (3D curved) transparent covers.

[0011] To that end the method according to the invention is characterized in that the method comprises a step of making through-slots in the chip.

[0012] By making through-slots in the chip, the chip is divided in several connected ‘flaps’. Each of these flaps can flex (bend) independent from others, When the chip is a solar cell with one side being the anode and the other side the cathode, each flap can bend while anode side and the cathode side stay interconnected. When the chip is an electronic chip interconnection lines (wires) between the flaps stay available for interconnection. The through-slots thus enable the chip to be bend or flex in two directions, while interconnection between the flaps stay possible.

[0013] It is noted that when forming such a through-slot, a small area bordering the through slot will become inactive. However, as known to the skilled artisan, this is also the case when several separate chips are bordering each other, as any border (several microns to tens of microns) of a chip becomes unavailable for electronic processes due to the high number of recombination sites and crystal imperfections occurring there.

[0014] In an embodiment of the method according to the invention while forming the through-slots, material is removed from the chip.

[0015] When forming the through-slots, for example by laser cutting, typically material is removed (ablated or cut-out). This can equally well happen using other machining techniques, such as water jet cutting, or chemical techniques such as (anisotropic)

etching. In the latter case it may be well combined with wafer techniques in which also the metallization etc. is formed.

[0016] In a further embodiment of the method according to the invention, as a result of the removal of material, in curved condition no parts of the chip overlaps with another part.

[0017] By modifying (cutting away) the area of the chip such, that in curved condition no parts of the chip touch each other or overlap each other, the thickness of the curved chip is identical to the non-curved chip. Also, no shorts between anode and cathode will occur.

[0018] In another embodiment of the method according to the invention at least one of the through-slots is completely surrounded by the periphery of the chip.

[0019] Here the through-slot is completely within the periphery of the chip. Forming, for example, two perpendicular through-slows intersecting each other, four flaps are formed that are held together at the edges. In the case of a solar cell the edges can be used to contact neighboring cells using, for example, finger electrodes.

[0020] In a preferred embodiment of the method according to the invention at least one of the through-slots intersects the periphery of the chip.

[0021] This results in several flap held together at, for example, the center. In the case of a solar cell the anode and the cathode can be contacted using, for example, a back- contact foil contacting electrodes in the center, a method of interconnecting cells known to the skilled artisan.

[0022] In another embodiment of the method according to the invention the chip is a solar cell.

[0023] Especially solar cells (also known as photovoltaic cells) are typically large chips (tens of square centimeters). When such large chips are used in solar vehicles or building integrated photovoltaic systems (BIPS), there is often a desire to curve them in two directions (for efficiency or esthetic reasons). As an example the solar panel of a solar car such as the Lightyear 1, sold by Atlas Technologies, Helmond, the Netherlands, is curved in two directions. Such curved large cells benefit from this invention as it enables the use of much larger cells using less interconnections.

Brief description of the drawings.

[0024] The invention is now elucidated using figures, in which identical reference signs indicate corresponding features. To that end: Figure 1A schematically shows a chip with four through-slots from the periphery inwards, Figure 1B schematically shows a chip with a multitude of through-slots, Figure 1C schematically shows a chip with four through-slots from the center outwards, Figure 1D schematically shows a chip with a through-slot in the form of a spiral, Figure 1E schematically shows a chip with fractal-like through-slots. and Figure 2 schematically shows a detail of the end of a through-slot.

Detailed description of the invention.

[0025] Figure 1A schematically shows a chip with four through-slots from the periphery inwards.

[0026] Here a chip is formed in which four flaps 1, 2, 3 and 4 are connected by a common center 5. Each of the flaps can now show curvature around its individually axis.

The requirement that for a whole chip curvature may only occur in one direction is now that curvature for each flap may occur in one direction, but that the curvature of different flaps may occur in different directions. For a solar cell the centerpart is the most convenient place to position electrodes (anode, cathode) upon, as it shows the smallest average distance from any of the parts of the chip, and thus the lowest resistivity. For an electronic chip the centerpart is the part where all interconnections between circuitry on the flaps must pass, but the electrodes where the ‘bumps’ are connected to the lead frame

[0027] Figure 1B schematically shows a chip with a multitude of through-slots.

[0028] A chip with a multitude of through-slots in a form resembling a fish-bone structure offer a large degree of freedom, as this implies a multitude flaps, each with its own curvature.

[0029] Figure 1C schematically shows a chip with four through-slots from the center outwards,

[0030] Instead of four flaps connected by a common center, here four flaps are shown with a common periphery

[0031] Figure 1D schematically shows a chip with a through-slot in the form of a spiral.

[0032] The through-slot need not be a straight line, but can also be a curved or a angular line, depending on the requirements.

[0033] Figure 1E schematically shows a chip with fractal-like through-slots.

[0034] Here the through-slots are formed in a fractal like pattern, dividing the chip in a multitude of flaps, offering high flexibility of the chip. 5 [0035] Figure 2 schematically shows a detail of the end of a through-slot.

[0036] At the end of the through-slot where it ends in the chip, mechanical stresses concentrate, possibly leading to fracture etc. To avoid this, said end is best formed such, that no sharp edges occur, but for example ending as a small circular hole, as shown in this figure 2 and figure 1A.

Cited non-patent literature. [-2-] “Ultra-thin chips for high-performance flexible electronics”, Gupta, S et al. . npj Flex Electron 2, 8 (2018). nttps://doi.org/10.1038/s41528-018-0021-5.

Claims (6)

Conclusions. A method for producing chips that can be bent in two directions, the chips having a periphery, the method comprising a step of providing chips, the method characterized in that the method comprising a step of making through slots (6, 7, 8, 9) in the chips. The method of claim 1, wherein material is removed from the chip during the through-slot making step. A method according to claim 2, wherein no parts of the chip overlap with another part as a result of the removal of material in the bent state. A method according to any one of the preceding claims, wherein at least one of the through-slits is completely surrounded by the periphery of the chip. A method according to any one of the preceding claims, wherein at least one of the through-slits intersects the periphery of the chip. A method according to any one of the preceding claims, wherein the chip is a photovoltaic cell.