Flip MEMS three-dimensional force sensor and decoupling method thereof

Abstract

This invention discloses a flip-chip MEMS three-dimensional force sensor and its decoupling method, belonging to the field of multi-dimensional force sensor technology in microelectromechanical systems (MEMS). The flip-chip MEMS three-dimensional force sensor includes a sensor chip, which, from top to bottom, comprises a force-transmitting boss, a deformable body, and an adapter plate. The deformable body has multiple force-transmitting pillars fixedly connected to the force-transmitting bosses on its front side, and is bonded to the adapter plate on its back side. First to fourth stress concentration grooves are provided on the back side of the deformable body corresponding to the outer edges of the force-transmitting pillars. First to fourth piezoresistors are respectively provided between the first and fourth stress concentration grooves, between the second and third stress concentration grooves, between the third and fourth stress concentration grooves, and between the fourth stress concentration groove and the first stress concentration groove. A fifth piezoresistor is provided between the fourth piezoresistor and the edge of the deformable body, and a sixth piezoresistor is provided between the second piezoresistor and the edge of the deformable body. This invention achieves high-sensitivity detection of three-dimensional forces and decoupling of three-dimensional forces.

Description

Technical Field

[0001] This invention belongs to the field of microelectromechanical systems (MEMS) multidimensional force sensor technology, specifically relating to a flip-chip MEMS three-dimensional force sensor and its decoupling method. Background Technology

[0002] In recent years, humanoid robots have developed rapidly, moving from verifying the feasibility of movement to the critical stage of practical application. Core applications such as industrial assembly, home services, and medical assistance all require robots to possess the tactile perception and precise control capabilities of a human-like dexterous hand. The tactile essence of a robot's dexterous hand lies in the analysis of multidimensional information about contact forces. Without this multidimensional force perception, the dexterous hand would be like a blind man feeling an elephant, unable to precisely control its movements, leading to operational failures or damage to objects. Therefore, the tactile performance of a humanoid robot's dexterous hand directly depends on the performance limit of its multidimensional force sensor, which places higher demands on the sensor's sensitivity, integration, reliability, and miniaturization.

[0003] Currently, mainstream micro-electro-mechanical system (MEMS) 3D force sensors generally employ solid bosses or force-transmitting columns in contact with the deformable body surface. This is essentially a surface-contact loading force transmission method. This type of force transmission is prone to force dispersion and loss during transmission, and it is difficult to achieve effective stress concentration. The resulting low stress amplitude in the deformable body directly limits the sensor's detection sensitivity. While some existing technologies attempt to optimize stress distribution and improve stress concentration by incorporating grooves or beams on the deformable body surface, the layout of these grooves and beams lacks specificity and does not match the actual stress location of the force transmission structure. This results in neither precise stress concentration nor effective release of redundant stress in the deformable body. The poor synergy between stress concentration and release fails to further improve the stress amplitude of the deformable body, making it difficult to meet the high detection sensitivity requirements of MEMS 3D force sensors in high-end micro-detection and precision measurement and control scenarios. Summary of the Invention

[0004] This invention provides a flip-chip MEMS three-dimensional force sensor and its decoupling method, achieving high sensitivity and high reliability detection of three-dimensional forces, as well as efficient decoupling of three-dimensional forces.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a flip-chip MEMS three-dimensional force sensor, including a sensor chip and two fixed resistors. The sensor chip includes a force-transmitting boss, a deformable body and an adapter plate arranged from top to bottom.

[0007] The front of the deformable body is provided with multiple force transmission columns, which are fixedly connected to the force transmission boss; the back of the deformable body is bonded to the front of the adapter plate.

[0008] The back of the deformable body is provided with a first set of stress concentration grooves at the outer edge of the force transmission column. The first set of stress concentration grooves includes a first stress concentration groove, a second stress concentration groove, a third stress concentration groove and a fourth stress concentration groove.

[0009] A first varistor is provided between the first stress concentration groove and the fourth stress concentration groove; a second varistor is provided between the second stress concentration groove and the third stress concentration groove; a third varistor is provided between the third stress concentration groove and the fourth stress concentration groove; a fourth varistor is provided between the first stress concentration groove and the second stress concentration groove; a fifth varistor is provided between the first varistor and the edge of the deformable body; and a sixth varistor is provided between the second varistor and the edge of the deformable body.

[0010] The first and second varistors are connected in series to form the first branch, the third and fourth varistors are connected in series to form the second branch, and the fifth and sixth varistors are connected in series to form the third branch.

[0011] Two fixed resistors are connected in series to form the fourth branch, and the first, second, third and fourth branches are connected in parallel to form a decoupling circuit;

[0012] A second set of stress concentration grooves is installed outside the first set of stress concentration grooves.

[0013] Furthermore, the front of the adapter board has a first square groove and four second square grooves surrounding the first square groove. The orthographic projections of the first varistor, the second varistor, the third varistor and the fourth varistor on the front of the adapter board are all located in the first square groove.

[0014] The orthographic projections of the fifth and sixth varistors on the front of the adapter plate are located in two opposite second square slots.

[0015] Furthermore, the second set of stress concentration grooves includes a fifth stress concentration groove, a sixth stress concentration groove, a seventh stress concentration groove, and an eighth stress concentration groove. The second set of stress concentration grooves is arranged around the first set of stress concentration grooves, and the orthographic projection of the outer edge of the second set of stress concentration grooves falls on the edge of the first square groove.

[0016] Furthermore, a spatial rectangular coordinate system is established with the geometric center of the deformable body's front as the origin. The X-axis and Y-axis of the spatial rectangular coordinate system are perpendicular to each other and both are located on the front of the deformable body. The Z-axis of the spatial rectangular coordinate system is perpendicular to the front of the deformable body.

[0017] The first and second varistors are symmetrically arranged on both sides of the Y-axis of the deformable body, and the main varistor grids of the first and second varistors both extend along the X-axis direction.

[0018] The third and fourth varistors are symmetrically arranged on both sides of the X-axis of the deformable body, and the main varistor grids of the third and fourth varistors extend along the Y-axis.

[0019] The fifth and sixth varistors are symmetrically arranged on both sides of the Y-axis of the deformable body, and the main varistor grid direction of the fifth varistor and the main varistor grid direction of the sixth varistor are perpendicular to each other. The fifth, first, second and sixth varistors are arranged sequentially along the X-axis.

[0020] Furthermore, it also includes a flexible cap, on the back of which is provided a double-stage boss, and on the front of which is provided a slot, and the double-stage boss and the slot are connected by a tenon and mortise joint.

[0021] Furthermore, the adapter plate is provided with eight through holes, and conductive posts are provided in the through holes; the back of the deformable body is provided with a first electrode, a second electrode, a third electrode, a fourth electrode, a fifth electrode, a sixth electrode, a seventh electrode, and an eighth electrode, which are electrically connected to the eight conductive posts respectively.

[0022] Furthermore, the first terminals of the first, fourth, and fifth varistors are all connected to the first terminal of the fourth branch through the first electrode;

[0023] The second terminal of the first varistor is connected to the first terminal of the second varistor through the eighth electrode and the fourth electrode; the second terminal of the fourth varistor is connected to the first terminal of the third varistor through the second electrode and the sixth electrode; and the fifth varistor is connected to the first terminal of the sixth varistor through the seventh electrode and the third electrode.

[0024] The second, third, and sixth varistors are all connected to the second terminal of the fourth branch via the fifth electrode.

[0025] Furthermore, the through holes are vertically aligned with the first electrode, second electrode, third electrode, fourth electrode, fifth electrode, sixth electrode, seventh electrode, and eighth electrode, respectively.

[0026] Secondly, the present invention provides a decoupling method for a flip-chip MEMS three-dimensional force sensor, comprising the following steps:

[0027] Step 1: Power the decoupling circuit. The potential between the two fixed resistors is recorded as the reference potential; the difference between the potential between the first and second varistors and the reference potential is recorded as the first differential signal; the difference between the potential between the third and fourth varistors and the reference potential is recorded as the second differential signal; the difference between the potential between the fifth and sixth varistors and the reference potential is recorded as the third differential signal.

[0028] Step 2: Acquire the first differential signal, the second differential signal, and the third differential signal; calculate the magnitude and direction of the force in the X-axis direction based on the first differential signal; calculate the magnitude and direction of the force in the Y-axis direction based on the second differential signal; calculate the magnitude and direction of the force in the Z-axis direction based on the third differential signal.

[0029] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0030] This invention provides a flip-chip MEMS three-dimensional force sensor. A force-transmitting boss connects to multiple force-transmitting pillars on the front side of a deformable body to transmit force. Compared to existing solid boss loading methods where the force-transmitting boss directly contacts the deformable body, this method changes the contact loading from the entire surface to the contact loading of multiple force-transmitting pillars, reducing force loss. With the total height of the force-transmitting boss and pillars being the same as the solid boss, the stress on the back side of the deformable body is doubled. Furthermore, a first stress concentration groove, a second stress concentration groove, a third stress concentration groove, and a fourth stress concentration groove are respectively set on the outer edge of the four force-transmitting pillars on the front side of the deformable body, further increasing the stress concentration effect. The second set of stress concentration grooves further releases the stress on the back side of the deformable body, increasing the stress concentration and thus improving sensitivity.

[0031] Meanwhile, the flip-chip MEMS three-dimensional force sensor adopts a flip-chip design, with the back of the deformable body bonded to the adapter plate. This flip-chip structure avoids gold wire bonding and is connected vertically through conductive pillars. After packaging, the size is close to that of the sensor chip itself, which is conducive to the miniaturization of the sensor and improves the reliability of the sensor. After the deformable body is bonded to the adapter plate, the inside of the sensor chip becomes a sealed space, which helps to reduce interference from the external environment and improves reliability.

[0032] Furthermore, the first square groove and four second square grooves combine to form a capacitive groove. After the adapter plate is bonded to the deformable body, the area of ​​the deformable body directly opposite the capacitive groove in the vertical direction is the main deformation region. When a force is applied, eight stress concentration zones can be formed in the deformation region. Four of these stress concentration zones are located at the outer edge of each force transmission column directly opposite the back of the deformable body in the vertical direction, and the other four are located at the four second square grooves directly opposite the back of the deformable body in the vertical direction. However, existing square grooves can only form four stress concentration zones at the outer edge of the force transmission column directly opposite the back of the deformable body in the vertical direction, with a rapidly attenuating stress distribution area at the edge of the non-bonded area. Placing varistors in the rapidly attenuating stress distribution area can easily lead to stress exceeding the linear region of the varistor, shortened fatigue life, and unreliable measurement data. This invention arranges varistors in the eight stress concentration zones, which can avoid the above problems and also facilitates the decoupling of three-dimensional forces.

[0033] Furthermore, the six varistors are arranged symmetrically in pairs, which can control the heavily doped region and make the lead wires as similar and symmetrical as possible, so that the flip-chip MEMS three-dimensional force sensor has a very low zero point; at the same time, the resistance of the heavily doped leads is between a few ohms and tens of ohms, which reduces the attenuation of sensitivity.

[0034] Furthermore, the flexible cap is tenon-and-mortise connected to the force-transmitting boss, which increases the contact area between the flexible cap and the force-transmitting boss, achieving a more stable and reliable force transmission.

[0035] Furthermore, the first and second varistors are used to detect force along the X-axis, the third and fourth varistors are used to detect force along the Y-axis, and the fifth and sixth varistors are used to detect force along the Z-axis. These six varistors share two external fixed resistors to form a decoupling circuit, effectively reducing the number of external components and circuit complexity, which is beneficial for the miniaturization of MEMS three-dimensional force sensors.

[0036] Furthermore, the shared electrodes on the sensor chip reduce the number of vias, which is beneficial for the miniaturization of MEMS three-dimensional force sensors.

[0037] The decoupling method of the present invention obtains the decoupled differential signal through the decoupling circuit. Combining the stress distribution characteristics when applying X-axis force, Y-axis force or Z-axis force, and the cancellation characteristics of the decoupling circuit, a varistor is arranged in the stress concentration area to form a decoupling circuit, thereby achieving a good decoupling effect. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the main structure of the flip-chip MEMS three-dimensional force sensor provided by the present invention;

[0039] Figure 2This is a side view of the main structure of the flip-chip MEMS three-dimensional force sensor provided by the present invention;

[0040] Figure 3 An exploded view of the main structure of the flip-chip MEMS three-dimensional force sensor provided by this invention;

[0041] Figure 4 This is a schematic diagram of a force transmission boss;

[0042] Figure 5 This is a schematic diagram of a flexible cap;

[0043] Figure 6 This is a schematic diagram of the adapter board;

[0044] Figure 7 This is a frontal view of the deformable body;

[0045] Figure 8 This is a schematic diagram of the back of the deformable body;

[0046] Figure 9 This is a schematic diagram of a varistor bridge;

[0047] Figure 10 A schematic diagram of the deformation of the deformable body when a force is applied in the X-axis direction;

[0048] Figure 11 A schematic diagram of the deformation of the deformable body when a force is applied in the Z-axis direction;

[0049] Figure 12 This is a schematic diagram of two sets of stress concentration zones and stress analysis paths;

[0050] Figure 13 A schematic diagram of the stress distribution along the Y-axis path and the X-axis path when a force is applied to a three-dimensional force sensor with a conventional cubic groove.

[0051] Figure 14 This is a schematic diagram of the stress distribution along the Y-axis path and the X-axis path when the three-dimensional force sensor provided by this invention is subjected to an X-axis force.

[0052] In the attached diagram: 1. Deformable body; 2. Force-transmitting boss; 3. Flexible cap; 4. Adapter plate; 21. Slot; 31. Double-stage boss; 41. First square slot; 42. Second square slot; 43. Through hole; 51. X-axis path; 52. Y-axis path; 61. First stress concentration area; 62. Second stress concentration area; 63. Non-bonded area; 71. Fixed resistor; 111. First electrode; 112. Second electrode; 113. Third electrode; 114. Fourth electrode; 115. Fifth electrode; 116. Sixth electrode; 117. Seventh electrode; 118. Eighth electrode; 121. First varistor; 122. Second varistor; 123. Third varistor; 124. Fourth varistor 125. Fifth varistor; 126. Sixth varistor; 131. First stress concentration groove; 132. Second stress concentration groove; 133. Third stress concentration groove; 134. Fourth stress concentration groove; 135. Fifth stress concentration groove; 136. Sixth stress concentration groove; 137. Seventh stress concentration groove; 138. Eighth stress concentration groove; 141. First lead; 142. Second lead; 143. Third lead; 144. Fourth lead; 145. Fifth lead; 146. Sixth lead; 147. Seventh lead; 148. Eighth lead; 149. Ninth lead; 1410. Tenth lead; 1411. Eleventh lead; 1412. Twelfth lead; 151. Force transmission column. Detailed Implementation

[0053] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0054] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0055] The detailed description of the embodiments of the present invention provided in the following figures is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the figures and embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0056] Reference Figures 1 to 3 A flip-chip MEMS three-dimensional force sensor includes a sensor chip, a flexible cap 3, and a fixed resistor 71. The sensor chip includes a deformable body 1, a force-transmitting boss 2, and an adapter plate 4.

[0057] Reference Figure 4 The force transmission boss 2 has a square slot 21 on its front side. (Refer to...) Figure 5The flexible cap 3 has a double-stage boss 31 on the back. The double-stage boss 31 is tenon-and-mortise connected to the slot 21. The back of the force transmission boss 2 is fixedly connected to the force transmission column 151 on the front of the deformable body 1. The front of the adapter plate 4 is keyed to the back of the deformable body 1.

[0058] Reference Figure 6 The adapter board 4 has a capacitance groove at the center of its front side. The capacitance groove is composed of a first square groove 41 in the middle and a second square groove 42 around the first square groove 41. The cross-sectional area of ​​the first square groove 41 is larger than the cross-sectional area of ​​the second square groove 42. There are eight through holes 43 around the capacitance groove. The through holes 43 are electroplated with metal to form conductive pillars to realize electrical conduction from the electrode to the external circuit board.

[0059] Reference Figure 7 Four force transmission columns 151 are fixed on the front of the deformable body 1. The four force transmission columns 151 are arranged in a centrally symmetrical manner and are evenly distributed around the geometric center of the front of the deformable body 1.

[0060] Reference Figure 8 The deformable body 1 has electrodes, a varistor, a stress concentration groove, and leads on its back side. The varistor is obtained by heavy boron ion doping, the leads are obtained by heavy boron ion doping, the electrodes are obtained by metal sputtering, and the stress concentration groove and the force transmission pillar 151 are obtained by etching.

[0061] The electrodes include a first electrode 111, a second electrode 112, a third electrode 113, a fourth electrode 114, a fifth electrode 115, a sixth electrode 116, a seventh electrode 117, and an eighth electrode 118; the varistor includes a first varistor 121, a second varistor 122, a third varistor 123, a fourth varistor 124, a fifth varistor 125, and a sixth varistor 126; the stress concentration grooves include a first group of stress concentration grooves and a second group of stress concentration grooves located outside the first group of stress concentration grooves, the first group of stress concentration grooves including a first stress concentration groove 13 with identical structure and size. 1. The second stress concentration groove 132, the third stress concentration groove 133, and the fourth stress concentration groove 134; the second group of stress concentration grooves includes the fifth stress concentration groove 135, the sixth stress concentration groove 136, the seventh stress concentration groove 137, and the eighth stress concentration groove 138, which have the same structure and size; the lead wires include the first lead wire 141, the second lead wire 142, the third lead wire 143, the fourth lead wire 144, the fifth lead wire 145, the sixth lead wire 146, the seventh lead wire 147, the eighth lead wire 148, the ninth lead wire 149, the tenth lead wire 1410, the eleventh lead wire 1411, and the twelfth lead wire 1412.

[0062] All stress concentration grooves are L-shaped. The first stress concentration groove 131, the second stress concentration groove 132, the third stress concentration groove 133, and the fourth stress concentration groove 134 are located in the middle position, forming a centrally symmetrical layout. The fifth stress concentration groove 135, the sixth stress concentration groove 136, the seventh stress concentration groove 137, and the eighth stress concentration groove 138 surround the first stress concentration groove 131, the second stress concentration groove 132, the third stress concentration groove 133, and the fourth stress concentration groove 134, forming a centrally symmetrical layout. The orthographic projection of their outer edges in the vertical direction falls on the edge of the first square groove 41.

[0063] A spatial rectangular coordinate system is established with the geometric center of the front of the deformable body 1 as the origin. The X-axis and Y-axis of the spatial rectangular coordinate system are perpendicular to each other and both are located on the front of the deformable body 1. The Z-axis of the spatial rectangular coordinate system is perpendicular to the front of the deformable body 1.

[0064] All varistors have the same structure, consisting of several parallel elongated strips and bent transition sections connecting them. The elongated strips are the main varistor grids, and the bent transition sections are all perpendicular to the main varistor grids and are wider than the main varistor grids. The first varistor 121 and the second varistor 122 are symmetrically arranged on both sides of the Y-axis of the deformable body 1 to detect forces in the X-axis direction, and their main varistor grids are arranged along the X-axis direction. The third varistor 123 and the fourth varistor 124 are symmetrical about the X-axis of the deformable body 1 to detect forces in the Y-axis direction, and their main varistor grids are arranged along the Y-axis direction. The fifth varistor 125 and the sixth varistor 126 are symmetrical about the Y-axis of the deformable body 1 to detect forces in the Z-axis direction. The main varistor grid of the fifth varistor 125 is arranged along the X-axis direction, and the main varistor grid of the sixth varistor 126 is arranged along the Y-axis direction. The fifth varistor 125, the first varistor 121, the second varistor 122 and the sixth varistor 126 are arranged sequentially along the X-axis.

[0065] The first varistor 121 is located between the first stress concentration groove 131 and the fourth stress concentration groove 134; the second varistor 122 is located between the second stress concentration groove 132 and the third stress concentration groove 133; the third varistor 123 is located between the third stress concentration groove 133 and the fourth stress concentration groove 134; and the fourth varistor 124 is located between the first stress concentration groove 131 and the second stress concentration groove 132. Simultaneously, the positions of the first varistor 121, the second varistor 122, the third varistor 123, and the fourth varistor 124 are vertically aligned with the outer edges of the four force transmission columns 151, and their orthogonal projections on the front of the adapter plate 4 are located within the first square groove 41. The orthogonal projections of the fifth varistor 125 and the sixth varistor 126 on the front of the adapter plate 4 are located within the two second square grooves 42, respectively.

[0066] Each lead is connected to an electrode at one end and a varistor at the other end. Each varistor is connected to two leads at each end, as shown in the following connection diagram:

[0067] The first end of the first varistor 121 is connected to the first electrode 111 via the first lead 141, and the second end is connected to the eighth electrode 118 via the second lead 142.

[0068] The first end of the second varistor 122 is connected to the fourth electrode 114 via the fourth lead 144, and the second end is connected to the fifth electrode 115 via the third lead 143.

[0069] The first end of the third varistor 123 is connected to the fifth electrode 115 via the fifth lead 145, and the second end is connected to the sixth electrode 116 via the sixth lead 146.

[0070] The first end of the fourth varistor 124 is connected to the first electrode 111 through the seventh lead 147, and the second end is connected to the second electrode 112 through the eighth lead 148.

[0071] The first end of the fifth varistor 125 is connected to the first electrode 111 through the ninth lead 149, and the second end is connected to the seventh electrode 117 through the tenth lead 1410.

[0072] The first end of the sixth varistor 126 is connected to the third electrode 113 through the twelfth lead 1412, and the second end is connected to the fifth electrode 115 through the eleventh lead 1411.

[0073] The first electrode 111 is connected to three leads simultaneously, the fifth electrode 115 is connected to three leads simultaneously, and the other electrodes are connected to only one lead.

[0074] The eight through holes 43 on the adapter plate 4 are vertically aligned with the positions of the first electrode 111, the second electrode 112, the third electrode 113, the fourth electrode 114, the fifth electrode 115, the sixth electrode 116, the seventh electrode 117, and the eighth electrode 118, respectively, and the diameter of the through holes 43 is slightly larger than the diameter of the electrodes.

[0075] Reference Figure 8 and Figure 9 The first varistor 121 and the second varistor 122 are connected in series through their respective eighth electrode 118 and fourth electrode 114 and external circuit to form a first series branch; the third varistor 123 and the fourth varistor 124 are connected in series through their respective sixth electrode 116 and second electrode 112 and external circuit to form a second series branch; the fifth varistor 125 and the sixth varistor 126 are connected in series through their respective seventh electrode 117 and third electrode 113 and external circuit to form a third series branch; the two fixed resistors 71 are connected in series to form a fourth series branch, and the four series branches are connected in parallel to form a decoupling circuit.

[0076] When the flip-chip MEMS three-dimensional force sensor is subjected to force, the force is applied to the flexible cap 3 and transmitted to the integral body formed by the deformable body 1 and the adapter plate 4 through the flexible cap 3 and the force transmission boss 2. The non-bonded area 63 of the capacitive groove on the deformable body 1, which is directly opposite in the vertical direction, is the main deformation position, which causes the resistance value of the corresponding piezoresistor on the back of the deformable body 1 to change. The decoupled differential signal is obtained through the decoupling circuit, realizing three-dimensional force sensing with high reliability, high sensitivity and low crosstalk.

[0077] The force transmission principle of the aforementioned flip-chip MEMS three-dimensional force sensor is as follows:

[0078] When an external force is applied, the force acts on the flexible cap 3 and is transmitted to the force transmission boss 2 through the flexible cap 3, causing deformation of the non-bonded area of ​​the deformable body 1 through the force transmission boss 2.

[0079] The double-stage boss 31 is tenon-and-mortise connected to the slot 21, enabling stable and accurate force loading. The front of the deformable body 1 has force-transmitting columns 151, and the force-transmitting boss 2 connects to these columns for force transmission. Compared to the common solid boss loading method (equivalent to removing the force-transmitting columns 151 in this invention, with the force-transmitting boss 2 directly contacting the deformable body 1 for loading), this method changes the contact loading from the entire surface to the contact loading of four force-transmitting columns 151, reducing force loss. With the total height of the force-transmitting boss 2 and the force-transmitting columns 151 being the same as the height of a common solid boss, the stress on the back of the deformable body 1 can be doubled. Furthermore, the back of the deformable body 1 has a first stress concentration groove 131, a second stress concentration groove 132, a third stress concentration groove 133, and a fourth stress concentration groove 134 positioned vertically opposite the outer edge of the four force-transmitting columns 151 on the front, further increasing the stress concentration effect. The second set of stress concentration grooves further releases the stress on the back of the deformable body 1, increasing the stress and improving the sensitivity of the three-dimensional force sensor.

[0080] When force is applied to the force-transmitting boss 2, the deformable body 1 deforms, and two sets of stress concentration areas are mainly generated on the back side of the deformable body 1: four first stress concentration areas 61 and four second stress concentration areas 62. The four first stress concentration areas 61 are located at the outer edges of the four force-transmitting columns 151 in the vertical direction, directly opposite the back side of the deformable body 1. The four second stress concentration areas 62 are located at the four second square grooves 42 in the vertical direction, directly opposite the back side of the deformable body. The first varistor 121, the second varistor 122, the third varistor 123, and the fourth varistor 124 are respectively arranged in the four first stress concentration areas 61, and the fifth varistor 125 and the sixth varistor 126 are respectively arranged in the two second stress concentration areas 62.

[0081] The above-mentioned decoupling method for flip-chip MEMS three-dimensional force sensors includes the following steps:

[0082] Step 1: Power on the decoupling circuit and acquire the first differential signal, the second differential signal, and the third differential signal. The differential signal between the potential U1 between the first varistor 121 and the second varistor 122 and the potential U0 between the two fixed resistors 71 is the voltage signal proportional to the force in the X-axis direction, and is denoted as the first differential signal. The differential signal between the potential U2 between the third varistor 123 and the fourth varistor 124 and the potential U0 between the two fixed resistors 71 is the voltage signal proportional to the force in the Y-axis direction, and is denoted as the second differential signal. The differential signal between the potential U3 between the fifth varistor 125 and the sixth varistor 126 and the potential U0 between the two fixed resistors 71 is the voltage signal proportional to the force in the Z-axis direction, and is denoted as the third differential signal.

[0083] Step 2: Calculate the magnitude and direction of the force in the X-axis direction based on the first differential signal; calculate the magnitude and direction of the force in the Y-axis direction based on the second differential signal; calculate the magnitude and direction of the force in the Z-axis direction based on the third differential signal.

[0084] The decoupling principle of this method is as follows:

[0085] If the decoupling circuit is powered by 5V, when no force is applied, due to the symmetrical arrangement of the varistors and leads, the potentials at the following locations are all 2.5V: U0 between the two fixed resistors 71, U1 between the first varistor 121 and the second varistor 122, U2 between the third varistor 123 and the fourth varistor 124, and U3 between the fifth varistor 125 and the sixth varistor 126. Therefore, all three differential signals are 0, meaning no force will be detected.

[0086] Reference Figure 10 When a force is applied to the flip-chip MEMS 3D force sensor along the X-axis, the second piezoresistor 122 and the first piezoresistor 121 experience the same stress, but opposite states (one under tension and the other under compression). The main piezoresistive grids of the first piezoresistor 121 and the second piezoresistor 122 are oriented in the same direction. One resistance increases while the other decreases, causing a corresponding change in the potential U1 between the first piezoresistor 121 and the second piezoresistor 122. This changes the first differential signal, detecting the force along the X-axis. The third piezoresistor 123 and the fourth piezoresistor 124 are in the neutral layer. The main piezoresistive grids of the third piezoresistor 123 and the fourth piezoresistor 124 are oriented in the same direction. Similarly, the third varistor 123 and the fourth varistor 124 are both without stress, and their resistance values ​​remain unchanged. Therefore, the potential U2 between the third varistor 123 and the fourth varistor 124 remains unchanged, the second differential signal is still 0, and no force in the Y-axis direction can be detected. The fifth varistor 125 and the sixth varistor 126 are subjected to the same stress, but in opposite states (one is under tension and the other is under compression). However, the main varistor grids of the fifth varistor 125 and the sixth varistor 126 are perpendicular to each other, and their resistance values ​​change in the same way. Therefore, the potential U3 between the fifth varistor 125 and the sixth varistor 126 remains unchanged, the third differential signal is still 0, and no force in the Z-axis direction can be detected.

[0087] Because deformable body 1 possesses axisymmetry in the X and Y axes, when a force is applied to the flip-chip MEMS three-dimensional force sensor in the Y-axis direction, the stresses on the third piezoresistor 123 and the fourth piezoresistor 124 are of the same magnitude but opposite in state (one is under tension and the other under compression). The main piezoresistor grids of the third piezoresistor 123 and the fourth piezoresistor 124 are in the same direction; one increases resistance while the other decreases resistance, causing a corresponding change in the potential U2 between them. This change in the second differential signal detects the force in the Y-axis direction. The first piezoresistor 121, the second piezoresistor 122, the fifth piezoresistor 125, and the sixth piezoresistor... All resistors 126 are in the neutral layer. There is no stress at the locations of the first varistor 121, the second varistor 122, the fifth varistor 125, and the sixth varistor 126. The main varistor grids of the first varistor 121 and the second varistor 122 are in the same direction, while the main varistor grids of the fifth varistor 125 and the sixth varistor 126 are perpendicular to each other, and their resistance values ​​remain unchanged. The potential U1 between the first varistor 121 and the second varistor 122 and the potential U3 between the fifth varistor 125 and the sixth varistor 126 remain unchanged. The first differential signal and the third differential signal are still 0, and no force in the X-axis direction or the Z-axis direction can be detected.

[0088] Reference Figure 11 When a force is applied to the flip-chip MEMS 3D force sensor along the Z-axis, the stress on the second piezoresistor 122 and the first piezoresistor 121 is the same, and their states are the same (both under tension or compression). The main piezoresistive wire grids of the first piezoresistor 121 and the second piezoresistor 122 are in the same direction, their resistance changes are the same, and the potential U1 between the first piezoresistor 121 and the second piezoresistor 122 remains unchanged. The first differential signal remains unchanged, and no force is detected along the X-axis. The stress on the third piezoresistor 123 and the fourth piezoresistor 124 is the same, and their states are the same. 24. The main varistor grids are in the same direction. The resistance changes of the third varistor 123 and the fourth varistor 124 are the same. The potential U2 between the third varistor 123 and the fourth varistor 124 remains unchanged. The second differential signal remains unchanged, and no force in the Y-axis direction can be detected. The stresses on the fifth varistor 125 and the sixth varistor 126 are the same, and their states are the same (both under tension or both under compression). However, the main varistor grids of the fifth varistor 125 and the sixth varistor 126 are perpendicular to each other. One resistance increases and the other resistance decreases. The potential U3 between the fifth varistor 125 and the sixth varistor 126 changes accordingly. The third differential signal changes, and a force in the Z-axis direction is detected.

[0089] This achieves the decoupling of forces along the X-axis, Y-axis, and Z-axis.

[0090] Force loading tests were conducted on the above-mentioned flip-chip MEMS three-dimensional force sensor, and the results are as follows:

[0091] Reference Figure 12 The line segment region located within the non-bonded region 63 on the back side of deformable body 1 and extending along the negative half-axis of the X-axis of deformable body 1 is denoted as X-axis path 51, and the line segment region located within the non-bonded region 63 of deformable body 1 and extending along the positive half-axis of the Y-axis of deformable body 1 is denoted as Y-axis path 52.

[0092] When a three-dimensional force sensor with a conventional cubic groove is subjected to a force along the X-axis, the stress distribution along the Y-axis path 52 and the X-axis path 51 is as follows: Figure 13 As shown, the stress on path 52 in the Y-axis direction is almost zero, while the stress on path 51 in the X-axis direction changes with the increase of the distance to the edge of the groove. Specifically, the stress first decreases sharply from a very large value, then slowly decreases to 0, then decreases to an extreme value, and finally gradually increases, with only a smooth and obvious stress concentration area.

[0093] When the flip-chip MEMS three-dimensional force sensor of the present invention is subjected to a force in the X-axis direction, the stress distribution of the Y-axis path 52 and the X-axis path 51 is as follows: Figure 14 As shown, the stress on path 52 in the Y-axis direction is almost zero, while the stress on path 51 in the X-axis direction changes with the increase of the distance to the edge of the groove. Specifically, the stress first increases to an extreme value, then decreases to 0, then decreases to an extreme value again, and finally gradually increases. Figure 14 and Figure 13 contrast, Figure 14 The stress distribution along path 51 in the X-axis direction shown has two smooth and distinct stress concentration regions, namely the areas near the two stress extrema. Compared to regions where stress decreases sharply, placing varistors in such stress concentration regions can avoid exceeding the linear region of the varistor, which can lead to shortened fatigue life and unreliable measurement data.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A flip-chip MEMS three-dimensional force sensor, characterized in that, It includes a sensor chip and two fixed resistors (71). The sensor chip includes a force transmission boss (2), a deformable body (1) and an adapter plate (4) arranged from top to bottom. The front of the deformable body (1) is provided with a plurality of force transmission columns (151), and the force transmission columns (151) are fixedly connected to the force transmission boss (2); the back of the deformable body (1) is bonded to the front of the adapter plate (4). The deformable body (1) has a first set of stress concentration grooves on its back side opposite the outer edge of the force transmission column (151). The first set of stress concentration grooves includes a first stress concentration groove (131), a second stress concentration groove (132), a third stress concentration groove (133), and a fourth stress concentration groove (134). A first varistor (121) is provided between the first stress concentration groove (131) and the fourth stress concentration groove (134); a second varistor (122) is provided between the second stress concentration groove (132) and the third stress concentration groove (133); a third varistor (123) is provided between the third stress concentration groove (133) and the fourth stress concentration groove (134); and a fourth varistor (124) is provided between the first stress concentration groove (131) and the second stress concentration groove (132). A fifth varistor (125) is provided between the first varistor (121) and the edge of the deformable body (1); and a sixth varistor (126) is provided between the second varistor (122) and the edge of the deformable body (1). The first varistor (121) and the second varistor (122) are connected in series to form the first branch, the third varistor (123) and the fourth varistor (124) are connected in series to form the second branch, and the fifth varistor (125) and the sixth varistor (126) are connected in series to form the third branch. The two fixed resistors (71) are connected in series to form a fourth branch, and the first branch, the second branch, the third branch and the fourth branch are connected in parallel to form a decoupling circuit; A second set of stress concentration grooves is provided outside the first set of stress concentration grooves; The adapter plate (4) has a first square groove (41) and four second square grooves (42) surrounding the first square groove (41) on its front side. The first varistor (121), the second varistor (122), the third varistor (123) and the fourth varistor (124) are all located in the first square groove (41) on the front side of the adapter plate (4). The fifth varistor (125) and the sixth varistor (126) are respectively located in two opposite second square slots (42) on the front of the adapter plate (4); The second group of stress concentration grooves includes a fifth stress concentration groove (135), a sixth stress concentration groove (136), a seventh stress concentration groove (137), and an eighth stress concentration groove (138). The second group of stress concentration grooves is arranged around the first group of stress concentration grooves. The orthographic projection of the outer edge of the second group of stress concentration grooves falls on the edge of the first square groove (41). All stress concentration grooves are L-shaped.

2. The flip-chip MEMS three-dimensional force sensor according to claim 1, characterized in that, A spatial rectangular coordinate system is established with the geometric center of the front of the deformable body (1) as the origin. The X-axis and Y-axis of the spatial rectangular coordinate system are perpendicular to each other and both are located on the front of the deformable body (1). The Z-axis of the spatial rectangular coordinate system is perpendicular to the front of the deformable body (1). The first varistor (121) and the second varistor (122) are symmetrically arranged on both sides of the Y-axis of the deformable body (1), and the main varistor grid of the first varistor (121) and the main varistor grid of the second varistor (122) both extend along the X-axis direction; The third varistor (123) and the fourth varistor (124) are symmetrically arranged on both sides of the X-axis of the deformable body (1), and the main varistor grid of the third varistor (123) and the main varistor grid of the fourth varistor (124) both extend along the Y-axis direction; The fifth varistor (125) and the sixth varistor (126) are symmetrically arranged on both sides of the Y-axis of the deformable body (1), and the main varistor grid direction of the fifth varistor (125) and the main varistor grid direction of the sixth varistor (126) are perpendicular to each other. The fifth varistor (125), the first varistor (121), the second varistor (122) and the sixth varistor (126) are arranged sequentially along the X-axis.

3. The inverted MEMS three-dimensional force sensor according to claim 1, characterized in that, It also includes a flexible cap (3), the back of which is provided with a double-stage boss (31), and the front of the force transmission boss (2) is provided with a slot (21), and the double-stage boss (31) is mortised and tenoned with the slot (21).

4. A flip-chip MEMS three-dimensional force sensor according to claim 1, characterized in that, The adapter plate (4) is provided with eight through holes (43), and conductive posts are provided in the through holes (43); the deformable body (1) is provided with a first electrode (111), a second electrode (112), a third electrode (113), a fourth electrode (114), a fifth electrode (115), a sixth electrode (116), a seventh electrode (117), and an eighth electrode (118) on the back side, and the first electrode (111), the second electrode (112), the third electrode (113), the fourth electrode (114), the fifth electrode (115), the sixth electrode (116), the seventh electrode (117), and the eighth electrode (118) are electrically connected to the eight conductive posts respectively.

5. A flip-chip MEMS three-dimensional force sensor according to claim 4, characterized in that, The first terminals of the first varistor (121), the fourth varistor (124), and the fifth varistor (125) are all connected to the first terminal of the fourth branch through the first electrode (111); The second end of the first varistor (121) is connected to the first end of the second varistor (122) through the eighth electrode (118) and the fourth electrode (114). The second end of the fourth varistor (124) is connected to the first end of the third varistor (123) through the second electrode (112) and the sixth electrode (116). The second end of the fifth varistor (125) is connected to the first end of the sixth varistor (126) through the seventh electrode (117) and the third electrode (113). The second end of the second varistor (122), the third varistor (123) and the sixth varistor (126) are all connected to the second end of the fourth branch through the fifth electrode (115).

6. A flip-chip MEMS three-dimensional force sensor according to claim 4, characterized in that, The through hole (43) is vertically aligned with the first electrode (111), the second electrode (112), the third electrode (113), the fourth electrode (114), the fifth electrode (115), the sixth electrode (116), the seventh electrode (117), and the eighth electrode (118), respectively.

7. A decoupling method for a flip-chip MEMS three-dimensional force sensor according to any one of claims 1 to 6, characterized in that, Includes the following steps: Step 1: Power the decoupling circuit. The potential between the two fixed resistors (71) is recorded as the reference potential. The difference between the potential between the first varistor (121) and the second varistor (122) and the reference potential is recorded as the first differential signal. The difference between the potential between the third varistor (123) and the fourth varistor (124) and the reference potential is recorded as the second differential signal. The difference between the potential between the fifth varistor (125) and the sixth varistor (126) and the reference potential is recorded as the third differential signal. Step 2: Acquire the first differential signal, the second differential signal, and the third differential signal; calculate the magnitude and direction of the force in the X-axis direction based on the first differential signal; calculate the magnitude and direction of the force in the Y-axis direction based on the second differential signal; calculate the magnitude and direction of the force in the Z-axis direction based on the third differential signal.

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