Force sensing system and force sensor thereof

Abstract

The force sensor includes a first substrate, a second substrate, and a piezoresistive element. The first substrate has an avoidance portion. The second substrate is disposed on the first substrate and has a suspended portion that at least partially covers the avoidance portion. The piezoresistive element is disposed on the second substrate and has a first end portion arranged on the suspended portion of the second substrate. The suspended portion is configured to bend toward the avoidance portion in response to an external force, wherein at least one electrical parameter of the piezoresistive element changes in response to the external force.

Description

Attorney Docket No. 5199-0421PWO1FORCE SENSING SYSTEM AND FORCE SENSOR THEREOFCROSS REFERENCE TO RELATED APPLICATIONSThis application claims the benefit of U.S. Patent Application No. 63 / 704,017, filed October 6, 2024, the entirety of which is incorporated by reference herein.TECHNICAL FIELD

[0001] The present invention relates to a force sensing system and a force sensor thereof, and more particularly to a force sensing system with a piezoresistive element and a force sensor suitable for the system.BACKGROUND

[0002] A force sensor converts mechanical force into an electrical signal, thereby enabling accurate measurement and control of force. It has been widely applied and plays an important role in various fields. For example, a force sensor can be used for measuring pressure, torque, or acceleration, and can be correspondingly applied to motion analysis or weight measurement.

[0003] In recent years, force sensors have also been applied to physiological signal detection in healthcare (for example, pulse pressure) or to high-precision measurements in automation control (for example, touch detection of robotic arms). As the applications of force sensors have become increasingly precise and miniaturized, both the force sensors and the corresponding force sensing systems face significant challenges.SUMMARY

[0004] The present invention provides a force sensing system and a force sensor thereof to effectively solve the aforementioned problems.Attorney Docket No. 5199-0421PWO1

[0005] In one aspect of the present invention, a force sensor is provided. The force sensor includes a first substrate, a second substrate, and a piezoresistive element. The first substrate has an avoidance portion. The second substrate is disposed on the first substrate and has a suspended portion that at least partially covers the avoidance portion. The piezoresistive element is disposed on the second substrate and has a first end portion arranged on the suspended portion of the second substrate. The suspended portion is configured to bend toward the avoidance portion in response to an external force, wherein at least one electrical parameter of the piezoresistive element changes in response to the external force.

[0006] In an embodiment, the avoidance portion includes a through hole penetrating the first substrate.

[0007] In an embodiment, the avoidance portion includes a recessed space formed on the first substrate.

[0008] In an embodiment, the force sensor further includes a flexible layer disposed between the piezoresistive element and the second substrate.

[0009] In an embodiment, the second substrate includes a conductive circuit electrically coupled to the piezoresistive element.

[0010] In an embodiment, the piezoresistive element further includes a second end portion, and the projection of the second end portion onto the first substrate does not overlap with the avoidance portion.

[0011] In an embodiment, the at least one electrical parameter includes a resistance value of the piezoresistive element.

[0012] In an embodiment, the second substrate includes a body, and the suspended portion extends from a connecting portion of the body and has a free end opposite to the connecting portion. The piezoresistive element has a longitudinal direction parallel to the direction in which the suspended portion extends from the body.

[0013] In an embodiment, the body surrounds the suspended portion.Attorney Docket No. 5199-0421PWO1

[0014] In an embodiment, a U-shaped notch is formed between the body and the suspended portion.

[0015] In an embodiment, the body includes a conductive circuit at least partially extending along the U-shaped notch.

[0016] In another aspect of the present invention, a force sensing system is provided. The force sensing system includes a force sensor and a reading circuit. The force sensor includes a first substrate, a second substrate, and a piezoresistive element. The first substrate has an avoidance portion. The second substrate is disposed on the first substrate and has a suspended portion that at least partially covers the avoidance portion. The piezoresistive element is disposed on the second substrate and has a first end portion arranged on the suspended portion of the second substrate. The suspended portion is configured to bend toward the avoidance portion in response to an external force, wherein at least one electrical parameter of the piezoresistive element changes in response to the external force. The reading circuit is electrically coupled to the piezoresistive element and configured to read the at least one electrical parameter of the piezoresistive element, and to determine the value of the external force according to the variation of the at least one electrical parameter.

[0017] In an embodiment, the avoidance portion includes a through hole penetrating the first substrate.

[0018] In an embodiment, the avoidance portion includes a recessed space formed on the first substrate.

[0019] In an embodiment, the force sensing system further includes a flexible layer disposed between the piezoresistive element and the second substrate.

[0020] In an embodiment, the second substrate includes a conductive circuit, and the reading circuit is electrically coupled to the piezoresistive element via the conductive circuit.Attorney Docket No. 5199-0421PWO1

[0021] In an embodiment, the piezoresistive element further includes a second end portion, and the projection of the second end portion onto the first substrate does not overlap with the avoidance portion.

[0022] In an embodiment, the at least one electrical parameter includes the resistance value of the piezoresistive element, and the reading circuit includes at least a Wheatstone bridge.

[0023] In an embodiment, the second substrate includes a body, and the suspended portion extends from a connecting portion of the body and has a free end opposite to the connecting portion. The piezoresistive element has a longitudinal direction parallel to the direction in which the suspended portion extends from the body.

[0024] In an embodiment, the body surrounds the suspended portion.

[0025] In an embodiment, a U-shaped notch is formed between the body and the suspended portion.

[0026] In an embodiment, the body includes a conductive circuit at least partially extending along the U-shaped notch.

[0027] In summary, the present invention discloses a circuit component serving as a force sensing system. The force sensing system includes the force sensor of the present invention. The force sensor includes the second substrate, the first substrate, and the piezoresistive element. The second substrate has a suspended portion disposed above the avoidance portion of the first substrate. The piezoresistive element is disposed on the suspended portion. When the force sensor is subjected to a force, the suspended portion bends toward the avoidance portion, thereby causing tensile stress on the piezoresistive element disposed on the suspended portion. Through the suspended portion and the piezoresistive element, the magnitude of the force can be measured more sensitively. Furthermore, the first substrate provides mechanical support and allows the suspended portion of the second substrate to undergo more significant deformation when subj ected to a force, thereby amplifying the change in theAttorney Docket No. 5199-0421PWO1 electrical parameter of the piezoresistive element. The variation of the electrical parameter caused by the applied force is measured by the reading circuit of the force sensing system, and the force is calculated. The piezoresistive element and the reading circuit are miniaturized through mature circuit manufacturing processes.BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are presented to help describe various aspects of the present invention. In order to simplify the accompanying drawings and highlight the contents to be presented in the accompanying drawings, conventional structures or elements in the accompanying drawings may be drawn in a simple schematic way or may be omitted. For example, a number of elements may be singular or plural. These accompanying drawings are provided merely to explain these aspects and not to limit them.

[0029] FIG. 1 is a schematic diagram of a force sensor according to an embodiment of the present invention.

[0030] FIGS. 2A and 2B are schematic diagrams of an embodiment of the present invention in which the first substrate has a recessed space forming the avoidance portion.

[0031] FIGS. 3A and 3B are schematic diagrams of an embodiment of the present invention in which the first substrate has a through hole forming the avoidance portion.

[0032] FIG. 4 is a schematic diagram illustrating the layering of the second substrate and the first substrate according to an embodiment of the present invention.

[0033] FIG. 5 is a top view of the second substrate according to an embodiment of the present invention.Attorney Docket No. 5199-0421PWO1

[0034] FIG. 6 is a schematic diagram illustrating different embodiments of the suspended portion of the second substrate according to an embodiment of the present invention.

[0035] FIG. 7 is a top view of the second substrate according to an embodiment of the present invention.

[0036] FIG. 8 is a schematic diagram of the piezoresistive material disposed on the second substrate according to an embodiment of the present invention.

[0037] FIG. 9 is a schematic diagram of the second substrate having a conductive circuit and a reference element according to an embodiment of the present invention.

[0038] FIG. 10 is a schematic diagram of a flexible layer disposed between the piezoresistive material and the second substrate according to an embodiment of the present invention.

[0039] FIG. 11 is a block diagram of a force sensing system according to an embodiment of the present invention.DETAILED DESCRIPTION

[0040] Any reference to elements using terms such as ’‘first” and “second” herein generally does not limit the number or order of these elements. Conversely, these names are used herein as a convenient way to distinguish two or more elements or element instances. Therefore, it should be understood that the terms “first” and “second” in the request item do not necessarily correspond to the same names in the written description. Furthermore, it should be understood that references to the first element and the second element do not indicate that only two elements can be used or that the first element needs to precede the second element. Open terms such as “include”, “comprise”, “have”, “contain”, and the like used herein means including but not limit to.Attorney Docket No. 5199-0421PWO1

[0041] The term ‘‘coupled” is used herein to refer to direct or indirect electrical coupling between two structures. For example, in an example of indirect electrical coupling, one structure may be coupled with another structure through a passive element such as a resistor, a capacitor, or an inductor.

[0042] In the present invention, the term such as “exemplar} ” or “for example” is used to represent “giving an example, instance, or description”. Any implementation or aspect described herein as “exemplary” or “for example” is not necessarily to be construed as preferred or advantageous over other aspects of the present invention. The terms “about” and “approximately” as used herein with respect to a specified value or characteristic are intended to represent within a value (for example, 10%) of the specified value or characteristic.

[0043] The force sensor of the present invention may, for example, be integrated into a medical sensing device. For instance, it may be incorporated to measure blood pressure based on micro-pulsations at the body surface. On the other hand, the force sensor of the present invention may, for example, be integrated into the gripping end of a robotic arm to serve as a touch sensor or a gripping force sensor. It should be noted that the above applications are merely illustrative examples of application fields of the force sensor of the present invention and are not intended to limit the application scope or items of the force sensor of the present invention.

[0044] In one aspect of the present invention, a force sensor is provided. As show n in FIG. 1, the force sensor 100 includes a first substrate 110, a second substrate 120, and a piezoresistive element 130. The first substrate 110 has an avoidance portion 111. The second substrate 120 is disposed on the first substrate 110 and has a suspended portion 121 at least partially covering the avoidance portion 111. The piezoresistive element 130 is disposed on the second substrate 120 and has a first end portion 131 arranged on the suspended portion 121 of the second substrate 120.Attorney Docket No. 5199-0421PWO1

[0045] In an embodiment, the material of the first substrate 110 is selected from, for example, plastic, metal, fiberglass, glass, or composite materials (such as FR-4, BT, ABF. or MIS) with mechanical strength. The avoidance portion 111 of the first substrate 110 is formed in the substrate material by mechanical processing (e g., lathe machining). In an embodiment, the first substrate 110 having the avoidance portion 111 is produced by molding. However, the present invention is not limited by the manufacturing method of the first substrate 110. The shape of the first substrate 110 is not limited to that illustrated in FIG. 1, and may be square, circular, or any other suitable shape. Similarly, the shape of the avoidance portion 111 of the first substrate 110 is not limited to that illustrated in FIG. 1, and may be square, circular, or any other suitable shape. Furthermore, the shape of the first substrate 110 and the shape of the avoidance portion 1 11 may be the same or different.

[0046] In an embodiment of the avoidance portion, the avoidance portion includes a recessed space formed on the first substrate 110. Specifically, as shown in FIGS. 2 A and 2B, the first substrate 110 includes a first substrate surface 1101 and a second substrate surface 1102. A recessed space 112 is formed on the first substrate surface 1101. The bottom 1121 of the recessed space 112 does not contact the second substrate surface 1102. In other words, the recessed space 112 is a cavity formed by recessing downward from the first substrate surface 1101 toward the second substrate surface 1102 without penetrating the second substrate surface 1102. More specifically, the thickness (DI) of the first substrate 110 is the distance between the first substrate surface 1101 and the second substrate surface 1102, and the depth (D2) of the recessed space 112 recessed from the first substrate surface 1101 is less than the thickness (DI) of the first substrate 110. The depth of the recessed space 112 is preferably configured so that, w hen the suspended portion 121 of the second substrate 120 bends toward the avoidance portion 111 under force, it does not touch the bottom 1121 of the recessed space 112. In other w ords, as shown in FIG. 2B, the recessed space 112 is preferablyAttorney Docket No. 5199-0421PWO1 arranged so as to not interfere with the deformation trajectory (Tl) of the suspended portion 121 of the second substrate 120 under force. Furthermore, when the suspended portion 121 is subjected to force, the piezoresistive element 130 will undergo bending, stretching, or deformation, thereby changing its electrical parameters. By using the recessed space 112, which does not penetrate the first substrate 110, as the avoidance portion 111 on the first substrate 110, the first substrate 110 maintains structural integrity and provides complete mechanical support. In addition, because the second substrate surface 1102 does not have a recess and is flat, or without notches, it provides support or protection against external forces or foreign objects acting from outside the second substrate surface 1102.

[0047] In another embodiment of the avoidance portion 111, the avoidance portion 1 11 is a through hole formed on the first substrate 110. Specifically, as shown in FIGS. 3A and 3B, the first substrate 110 includes a first substrate surface 1101 and a second substrate surface 1102. A through hole 113 penetrates from the first substrate surface 1101 to the second substrate surface 1102 of the first substrate 110. When the suspended portion 121 of the second substrate 120 bends toward the avoidance portion 111 under force, it is able to deform freely without interference at the through hole 113. The provision of the through hole 113 significantly reduces the required thickness of the first substrate 110, and the deformation of the suspended portion 121 of the second substrate 120 under force will not be interfered by the first substrate 110. Therefore, the deformation amplitude of the suspended portion 121 of the second substrate 120 is increased, thereby producing a larger or more significant signal variation in the piezoresistive element 130 disposed on the second substrate 120.

[0048] The second substrate 120 is a layer having rigidity less than that of the first substrate 110, or an elastic modulus greater than that of the first substrate 110. The material of the second substrate 120 is preferably selected from materials having insulating properties and mechanical strength (e.g., fracture resistance or ruptureAttorney Docket No. 5199-0421PWO1 resistance). In an embodiment, the material of the second substrate 120 is selected from, for example, FR-4, polyimide (PI), or polyethylene terephthalate (PET). It should be noted that the second substrate 120 and the first substrate 110 may also be made of the same material, with their respective elastic modulus, rigidity, or Young’s modulus adjusted by substrate thickness or composition ratios. The second substrate 120 is disposed on the first substrate 110. Specifically, as shown in FIG. 4, the second substrate 120 is disposed on the first substrate surface 1101 of the first substrate 110, and the second substrate 120 at least covers the avoidance portion 111 of the first substrate 110. The second substrate 120 is fixed on the first substrate 110 by bonding, riveting, pressing, or screwing, but is not limited thereto. The suspended portion 121 of the second substrate 120 is exemplarily defined as a portion of the second substrate 120 that is not supported by the first substrate 110. Specifically, as shown in FIG. 5, the second substrate 120 includes a body 122, and the suspended portion 121 extends from a connecting portion 125 of the body 122 and has a free end 1211 opposite to the connecting portion 125. The piezoresistive element 130 has a longitudinal direction 1301. which is parallel to the direction in which the suspended portion 121 extends from the body 122. The suspended portion 121 at least partially covers the avoidance portion 111 and is connected to the body 122 of the second substrate 120, which is supported by the first substrate 110. The suspended portion 121 is formed by cutting notches 123 on the second substrate 120, but is not limited thereto. In an embodiment, the total length (LI + L2 + L3) of the notches is preferably greater than the length (L4) of the portion of the second substrate 120 supported by the first substrate 110 so that the suspended portion 121 is able to deform more freely under force. Furthermore, the invention is not limited to the shape of the suspended portion 121, which may be U- shaped, polygonal, triangular, or circular, as shown in FIG. 6.

[0049] In an embodiment, the body 122 of the second substrate 120 surrounds the suspended portion 121. However, in another embodiment, as shown in FIG. 7, theAttorney Docket No. 5199-0421PWO1 body 122 is not surrounding the suspended portion 121. In the embodiment, the second substrate 120 has an edge 1201, which has an edge notch 1202 connected to the notch 123. The body 122 is arranged not to surround the suspended portion 121 via the edge notch 1202. By providing surrounding or non-surrounding configurations of the body 122 and the suspended portion 121 of the second substrate 120, different applications or force applying methods are achieved.

[0050] The piezoresistive element 130 is selected from, for example, a piezoelectric or piezoresistive material element that undergoes a change in voltage or impedance when subjected to mechanical stress (such as pressure or tension). The piezoresistive element 130 is disposed on the second substrate 120 and has a first end portion 131 disposed on the suspended portion 121 of the second substrate 120. Specifically, as shown in FIG. 8, the piezoresistive element 130 includes a first end portion 131 and a second end portion 132. The first end portion 131 is disposed on the suspended portion 121, and the second end portion 132 is disposed on a portion of the second substrate 120 supported by the first substrate 110. Therefore, the projection Pl 32 of the second end portion 132 onto the first substrate 110 does not overlap with the avoidance portion 111. As such, one part of the piezoresistive element 130 is supported by the first substrate 110, and another part deforms under force along with the suspended portion 121 and is subjected to mechanical stress along with the suspended portion 121. When the piezoresistive element 130 is subjected to mechanical stress (e.g., tension / stress generated between the deformed suspended portion 121 of the second substrate 120 and the fixed portion), its electrical parameters (e.g., voltage or impedance) change due to the material characteristics. Compared with the configuration in which the piezoresistive element 130 is entirely supported by the first substrate 110 (i.e., not disposed on the suspended portion 121), the suspended portion 121 of the present invention manifests the force applied to the piezoresistive element 130, thereby making the change in the electrical parameters of the piezoresistiveAttorney Docket No. 5199-0421PWO1 element 130 more significant. Accordingly, the signal -to-noise ratio, accuracy, or detection limit during measurement is improved (for example, enabling the detection of smaller forces).

[0051] In an embodiment, the second substrate 120 includes a conductive circuit electrically coupled to the piezoresistive element 130. As shown in FIG. 9, the conductive circuit 124 is disposed on the second substrate 120 by circuit fabrication processes, and the conductive circuit 124 extends at least partially along the notch 123. The conductive circuit 124 is connected to the piezoresistive element 130 by bonding pads, wire bonding, or any other conventional connection method. The conductive circuit 124 on the second substrate 120 improves the integration level of the force sensor 100 and avoids wiring disorder. Furthermore, by adopting mature circuit fabrication methods (e.g., etching, carving, or photolithography), the yield and stability of the force sensor 100 is improved. In the embodiment, the second substrate 120 further includes a reference element 140. The reference element 140 is electrically connected to the piezoresistive element 130 and forms, for example (but not limited to), a comparator or a Wheatstone bridge circuit. In an embodiment, the reference element 140 is selected from a resistor, capacitor, or other component with known electrical parameters. When the piezoresistive element 130 changes its electrical parameter (e.g., resistance) due to applied force, the reference element 140 serves as a reference to highlight the variation of the electrical parameter of the piezoresistive element 130.

[0052] In an embodiment, the force sensor further includes a flexible layer disposed between the piezoresistive element 130 and the second substrate 120. As shown in FIG. 10. the material of the flexible layer 150 may be polyimide (PI) or polyethylene terephthalate (PET). The mechanical rigidity of the flexible layer 150 is preferably between that of the first substrate 110 and the second substrate 120. The piezoresistive element 130 is disposed (e.g., by surface mounting or bonding) on the flexible layer 150, and the flexible layer 150 is disposed (e.g., by bonding) on theAttorney Docket No. 5199-0421PWO1 second substrate 120 so that the flexible layer 150 acts as an intermediate material between the piezoresistive element 130 and the second substrate 120. The flexible layer 150 can, for example, improve the stability of the piezoresistive element 130 disposed on the second substrate 120. In an embodiment, the piezoresistive material is combined with the flexible layer 150 first, and then disposed on the second substrate 120 via the flexible layer 150. Therefore, in terms of processing or fabrication, the reliability of mounting the piezoresistive material is improved. On the other hand, when the piezoresistive material deforms under force, the flexible layer 150 serves as a buffer between the second substrate 120 and the piezoresistive material, preventing breakage or other problems caused by excessive rigidity differences.

[0053] In summary’, the present invention discloses a force sensor 100 comprising a second substrate 120, a first substrate 1 10, and a piezoresistive element 130. The second substrate 120 has a suspended portion 121 disposed above the avoidance portion 111 of the first substrate 110. The piezoresistive element 130 is disposed on the suspended portion 121 . When the force sensor 100 is subjected to force, the suspended portion 121 bends toward the avoidance portion 111. thereby generating tensile stress on the piezoresistive element 130 disposed on the suspended portion 121. By means of the suspended portion 121 and the piezoresistive element 130, the magnitude of the applied force is measured more sensitively. Furthermore, the first substrate 110 provides mechanical structural support and enables the suspended portion 121 of the second substrate 120 to undergo more significant deformation when subjected to force, thereby amplifying the change in the electrical parameter of the piezoresistive element 130. The variation in the electrical parameter of the piezoresistive element 130 caused by the applied force is measured by the reading circuit of the force sensing system, thereby allowing the force to be calculated. The piezoresistive element 130 and the reading circuit are miniaturized by mature circuit fabrication processes.Attorney Docket No. 5199-0421PWO1

[0054] In another aspect of the present invention, a force sensing system is provided. As shown in FIG. 11, the force sensing system 10 includes the force sensor 100 of the present invention and a reading circuit 200. The reading circuit 200 is electrically coupled to the piezoresistive element 130 and is configured to read at least one electrical parameter (EP) of the piezoresistive element 130, and to determine the value of the external force according to the variation of the at least one electrical parameter (EP).

[0055] The selection of the reading circuit 200 depends on at least one electrical parameter of the piezoresistive element 130. For example, when the piezoresistive element 130 changes its electrical parameter in terms of resistance value due to applied force, the reading circuit 200 is configured to read the changed electrical parameter by a volt-ampere method or a bridge circuit configuration. Taking the volt-ampere method as an example, a known current source or voltage source is provided to the piezoresistive element 130, and the voltage across the piezoresistive element 130 or the current through the piezoresistive element 130 is measured, thereby measuring the resistance variation of the piezoresistive element 130. In an embodiment, the reading circuit 200 includes a bridge circuit, such as a Wheatstone bridge. In this embodiment, the reading circuit 200 utilizes the resistance balance principle of the bridge composed of resistors, calculates resistance variation of the bridge through a variable resistor, or calculates the resistance variation of the piezoresistive element 130 through a reference resistance value and the current flowing through the bridge. However, the piezoresistive element 130 of the present invention is not limited to resistance variation, and may also be measured by selecting a corresponding reading circuit 200 for voltage or capacitance variation.

[0056] In an embodiment, the reading circuit 200 is coupled to a computing element 300. The computing element 300 is selected from, for example, an FPGA, microprocessor, processor, ASIC, or any components that have computing capability.Attorney Docket No. 5199-0421PWO1The computing element 300 is configured to determine the force applied to the piezoresistive element 130 according to the variation of the electrical parameter measured by the reading circuit 200 by back-calculating based on the correlation between the material properties of the piezoresistive element 130 and its electrical parameters. In an embodiment, the computing element 300 may be a computer, an industrial computer, or any devices that have computing functionality. Through analog- to-digital conversion, the variation of the electrical parameter (EP) of the piezoresistive element 130 measured by the reading circuit 200 is converted from an analog value to a digital value and then provided to the computing element. It should be noted that the above is merely an example, and the computing element 300 is not limited to processing digital signals. The computing element performs computation through preloaded programs or instruction sets and obtains corresponding force information.

[0057] In summary, the present invention discloses a force sensing system 10 comprising a force sensor 100 and a reading circuit 200. The variation in the electrical parameter of the piezoresistive element 130 on the force sensor 100 caused by applied force is measured by the reading circuit 200 of the force sensing system 10, and the force value to be measured by the force sensor 100 can thereby be calculated. The piezoresistive element 130 and the reading circuit 200 are miniaturized by mature circuit fabrication processes.

[0058] The aforementioned description of the present invention is provided to enable a person of ordinary skill in the art to make or implement the present invention. Various modifications to the present invention will be apparent to a person skilled in the art, and the general principles defined herein can be applied to other variations without departing from the spirit or scope of the present invention. Therefore, the present invention is not intended to be limited to the examples described herein, but is to be in accord with the widest scope consistent with the principles and novel features of the invention herein.

Claims

Attorney Docket No. 5199-0421PWO1CLAIMSWhat is claimed is:

1. A force sensor comprising: a first substrate having an avoidance portion; a second substrate disposed on the first substrate and having a suspended portion at least partially covering the avoidance portion, wherein an elastic modulus of the first substrate is greater than that of the second substrate: and a piezoresistive element disposed on the second substrate and having a first end portion disposed on the suspended portion of the second substrate: wherein the suspended portion is configured to bend toward the avoidance portion in response to an external force, thereby causing at least one electrical parameter of the piezoresistive element to change.

2. The force sensor of claim 1 , wherein the avoidance portion includes a through hole penetrating the first substrate.

3. The force sensor of claim 1, wherein the avoidance portion includes a recessed space formed on the first substrate.

4. The force sensor of claim 1, further comprising a flexible layer disposed between the piezoresistive element and the second substrate.

5. The force sensor of claim 1, wherein the second substrate comprises a conductive circuit electrically coupled to the piezoresistive element.

6. The force sensor of claim 1, wherein the piezoresistive element further comprises a second end portion, and a projection of the second end portion onto the first substrateAttorney Docket No. 5199-0421PWO1 does not overlap with the avoidance portion.

7. The force sensor of claim 1. wherein the at least one electrical parameter includes a resistance value of the piezoresistive element.

8. The force sensor of claim 1. wherein the second substrate comprises a body, the suspended portion extending from a connecting portion of the body and having a free end opposite to the connecting portion; the piezoresistive element having a longitudinal direction parallel to a direction in which the suspended portion extends from the body.

9. The force sensor of claim 8, wherein the body surrounds the suspended portion.

10. The force sensor of claim 8, wherein a U-shaped notch is formed between the body and the suspended portion.

11. The force sensor of claim 10, wherein the body comprises a conductive circuit at least partially extending along the U-shaped notch.

12. A force sensing system, comprising: a force sensor, comprising: a first substrate having an avoidance portion; a second substrate disposed on the first substrate and having a suspended portion at least partially covering the avoidance portion; and a piezoresistive element disposed on the second substrate and having a first end portion disposed on the suspended portion of the second substrate; wherein the suspended portion is configured to bend toward the avoidance portion in response to an external force;Attorney Docket No. 5199-0421PWO1 wherein, in response to the external force, at least one electrical parameter of the piezoresistive element changes; and a reading circuit electrically coupled to the piezoresistive element and configured to read the at least one electrical parameter of the piezoresistive element and detennine a value of the external force according to a variation of the at least one electrical parameter.

13. The force sensing system of claim 12, wherein the avoidance portion includes a through hole penetrating the first substrate.

14. The force sensing system of claim 12, wherein the avoidance portion includes a recessed space formed on the first substrate.

15. The force sensing system of claim 12, further comprising a flexible layer disposed between the piezoresistive element and the second substrate.

16. The force sensing system of claim 12, wherein the second substrate comprises a conductive circuit, and the reading circuit is electrically coupled to the piezoresistive element via the conductive circuit.

17. The force sensing system of claim 12, wherein the piezoresistive element further comprises a second end portion, and a projection of the second end portion onto the first substrate does not overlap with the avoidance portion.

18. The force sensing system of claim 12, wherein the at least one electrical parameter includes a resistance value of the piezoresistive element, and the reading circuit comprises at least a Wheatstone bridge.Attorney Docket No. 5199-0421PWO119. The force sensing system of claim 12, wherein the second substrate comprises a body, the suspended portion extending from a connecting portion of the body and having a free end opposite to the connecting portion; the piezoresistive element having a longitudinal direction parallel to a direction in which the suspended portion extends from the body.

20. The force sensing system of claim 19, wherein the body surrounds the suspended portion.

21. The force sensing system of claim 19, wherein a U-shaped notch is formed between the body and the suspended portion.

22. The force sensing sy stem of claim 21, wherein the body comprises a conductive circuit at least partially extending along the U-shaped notch.

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