Integrated circuit stress sensor

Abstract

Described herein is an integrated circuit (100) including a semiconductor substrate (102). First and second piezoresistive sensors (108, 112) are located on or within the substrate (102), each having a respective sense axis (110, 114) extending in a first and second direction parallel to a surface (104) of the substrate (102), the second direction being perpendicular to the first direction. A third piezoresistive sensor (116) is located on or within the substrate (102) and has a respective sense axis (118) extending in a third direction parallel to the surface (104) of the substrate (102), which is neither parallel nor perpendicular to the first and second directions.

Description

Technical Field

[0001] This application generally relates to torque sensors, and more specifically to integrated circuit stress sensors.

Background Art

[0002] There are various types of torque sensors for measuring and recording torque on a rotating shaft. Many existing torque sensor systems are generally costly and / or include components for measuring a certain effect from the shaft, such as an electrical, magnetic, or optical effect, resulting in a bulky system. For example, Hall-based magnetic systems require a magnetized shaft or a magnet attached to the shaft, which are susceptible to interference from magnetic fields. Optical systems are complex to assemble and may require a special housing. Microelectromechanical systems (MEMS) torque sensors use piezoresistors attached outside an integrated circuit (IC) chip to measure the bending and / or torsion of the shaft. However, MEMS torque sensors require an external stand-alone readout and signal conditioning circuit mounted on a printed circuit board, resulting in a bulky system.

[0003] Other torque sensor systems include strain gauges attached to a rotating shaft of a structure. The strain gauge may include a metal piece or wire attached to the shaft via an adhesive. Such torque sensor systems also include signal conditioning circuit elements and a power supply mounted on the shaft. When the shaft is subjected to torque, the strain gauge stretches and sends a signal to the signal conditioning circuit elements. Thus, the strain gauge torque sensor system is also a bulky system that requires several separate components mounted on the shaft and separated from each other.

Summary of the Invention

[0004] In one example, an integrated circuit including a semiconductor substrate is described. The integrated circuit includes a first strain sensing sensor on or in the substrate having a first sensing axis extending in a first direction parallel to the surface of the substrate, and a second strain sensing sensor on or in the substrate having a second sensing axis extending in a second direction parallel to the surface of the substrate and perpendicular to the first direction. A third strain sensing sensor is on or in the substrate and has a third sensing axis extending in a third direction parallel to the surface of the substrate and neither parallel nor perpendicular to the first and second directions.

[0005] In another example, a system including an integrated circuit (IC) including a strain sensing sensor on or in a semiconductor substrate is described. The substrate has a certain crystal orientation, and each of the strain sensing sensors has a respective sensing axis oriented at a certain angle with respect to the crystal orientation of the substrate. The IC includes a sensing circuit configured to determine a change in resistance for each of the respective strain sensing sensors in response to deformation of the substrate. A communication device is coupled to the IC, and the communication device is configured to wirelessly communicate data representative of the deformation of the substrate in response to the change in resistance. A controller is coupled to the IC and the communication device and is configured to control communication with the communication device.

[0006] In yet another example, an integrated circuit (IC) including a strain sensing sensor on or in a semiconductor substrate having a certain crystal orientation is described. The strain sensing sensor includes a first strain sensing sensor on or in the substrate having a first sensing axis extending in a first direction parallel to the surface and the crystal orientation of the substrate. A second strain sensing sensor is on or in the substrate and has a second sensing axis extending in a second direction transverse to the crystal orientation of the substrate and parallel to the surface of the substrate, and the second direction is perpendicular to the first direction. A third strain sensing sensor is on or in the substrate and has a third sensing axis extending in a third direction parallel to the surface of the substrate and neither parallel nor perpendicular to the first and second directions. A sensing circuit is coupled to each of the first, second, and third strain sensing sensors, and the sensing circuit is configured to provide respective sensing signals, and the sensing signals represent changes in resistance of the respective first, second, and third strain sensing sensors in response to deformation of the substrate.

Brief Description of the Drawings

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[0030] An integrated circuit (IC) including a strain sensing sensor is described herein. The strain sensing sensor is configured to function in relation to a sensing circuit to measure stress components (e.g., normal and shear) in response to mechanical forces applied to the IC. The IC is coupled to a mechanical structure (e.g., a shaft, beam, feather key, lead frame, etc.) and adapted to measure torque or other stresses applied to such mechanical structure. The strain sensing sensor is formed on or within the surface of the substrate of the IC and has respective sensing axes oriented in different directions with respect to the crystal orientation of the substrate. Thus, the strain sensing sensor can be configured to measure deformations in the substrate in response to mechanical forces applied to the mechanical structure to which the IC is coupled via an adhesive, clamp, metal joint, adhesive joint, push or non-push fit joint, or otherwise experienced by the mechanical structure. The strain sensing sensor can include circuit components or devices formed on or within a semiconductor substrate. Examples of strain sensing components are active and passive components including bipolar transistors, complementary metal oxide semiconductor (CMOS) transistors, metal lines, piezoresistors, etc. The strain sensing components are mainly described as piezoresistive sensors in the following examples. However, other types of strain sensing components may be implemented in the ICs and SoCs described herein.

[0031] As a further example, a piezoresistive sensor is coupled to circuit elements that can be integrated within the sensor and an IC. For example, the piezoresistive sensor has respective resistance values that change in response to mechanical forces (e.g., shear and normal forces) received by the substrate. Thus, the circuit elements can be configured to determine an indication of the normal and shear forces based on the measured resistance values of the piezoresistive sensor. Also, the resistance values of the respective piezoresistive sensors can be used to correct for the impact of forces on associated circuit elements in the IC. In one example, the IC includes a temperature sensor integrated within the substrate in the vicinity of the piezoresistive sensor. The temperature sensor can provide a temperature signal representative of the substrate temperature. The circuit elements can be configured to adjust the measured resistance values in response to the temperature signal to reduce the temperature impact on the measured resistance values, and thus also reduce the temperature impact on the determined indication of the forces.

[0032] FIG. 1A is a block diagram of an integrated circuit (IC) 100. The IC 100 is adapted to couple to a mechanical structure (e.g., a shaft, beam, feather key, lead frame, etc.). The IC 100 includes a substrate 102 having a contact surface and an opposing mounting surface 104. The contact surface of the IC is adapted to couple the IC 100 to the mechanical structure by an adhesive, clamp, metal joint, adhesive joint, press fit, non-press fit, etc. The substrate 102 is made from a semiconductor material such as silicon, germanium, gallium arsenide, etc. The substrate has a crystal orientation (axis) that can extend in any direction (e.g., the x-direction, y-direction, z-direction, or combinations thereof) based on the material and formation of the substrate 102. In the example of FIG. 1A, the crystal orientation of the substrate 102 is represented by a crystal (or central) axis 106 that extends in the x-direction.

[0033] As an example, the substrate 102 is a semiconductor wafer formed from a single crystal rod, and thus the substrate surface is oriented with respect to the crystal plane. Miller indices, indicated by the curly brackets {}, are used to determine each of the planes in a cubic crystal. For example, the substrate can be a p-type (or n-type) semiconductor substrate cut on a {100} plane.

[0034] The exemplary IC 100 further includes piezoresistive sensors formed on or within the surface 104 of the substrate 102. For example, the first piezoresistive sensor 108 has a sensing axis 110 that extends in a first direction parallel to the mounting surface 104 of the substrate 102 and parallel to a crystal axis (e.g.,

[0100] or another crystal axis). The second piezoresistive sensor 112 has a sensing axis 114 that extends in a second direction parallel to the mounting surface 104 of the substrate 102 and perpendicular to the first direction of the first piezoresistive sensor 108. The third piezoresistive sensor 116 has a sensing axis 118 that extends in a third direction parallel to the mounting surface 104 of the substrate 102 and neither parallel nor perpendicular to the first and second directions of the first and second piezoresistive sensors 108 and 112, respectively. In one example, the sensing axis 118 can be oriented at an angle (e.g., about 45° from axes 110 and 114) that is approximately midway between the first and second directions of the respective sensing axes 110 and 114. In another example, the sensing axis 118 of the third piezoresistive sensor 116 can be oriented at other angles (e.g., 15°, 30°, 60°, 75°, etc.) with respect to the respective sensing axes 110 and 114. The arrangement of the piezoresistive sensors 108, 112, 116 on or within the substrate 102 is such that the orientation of each sensing axis can be parallel or perpendicular to the crystal axes of wafers cut in different crystal planes (e.g.,

[0110] crystal,

[0111] crystal), or can be oriented at other angles (e.g., 15°, 30°, 60°, 75°, etc.) with respect to those crystal axes.

[0035] Piezoelectric resistance sensors 108, 112, and 116 are coupled to a sensing (readout) circuit 120. For example, each of the piezoelectric resistance sensors 108, 112, and 116 has input and output terminals that are coupled to respective outputs and inputs of the sensing circuit 120. The sensing circuit 120 is configured to measure a change in resistance of each of the respective piezoelectric resistance sensors 108, 112, and 116. The change in resistance responds to a deformation of the substrate 102 from its normal (rest) state, which can be caused by, for example, a mechanical force (such as a compressive force, a tensile force, and / or a shear force) applied to the substrate 102. The sensing circuit 120 provides an output signal (sensing signal) representing longitudinal (e.g., compressive and / or tensile), normal, and shear forces in response to the measured change in resistance of each of the respective piezoelectric resistance sensors 108, 112, and 116. As described in the present application, the specific force measured by each piezoelectric resistance sensor 108, 112, and 116 depends on the orientation of the sensing axis of each piezoelectric resistance sensor with respect to the orientation of the crystal axis 106 of the substrate 102.

[0036] As a further example, the sensing axis 110 of the first piezoelectric resistance sensor 108 is oriented parallel to the orientation of the crystal axis 106 of the substrate 102 (e.g., parallel to the

[0100] crystal axis). The sensing axis 114 of the second piezoelectric resistance sensor 112 is oriented perpendicular to the orientation of the crystal axis 106 of the substrate 102 (e.g., perpendicular to the

[0100] crystal axis or parallel to the

[0010] axis). In this configuration, the piezoelectric resistance sensor 108 is configured such that a change in resistance in the first piezoelectric resistance sensor 108 represents a longitudinal (e.g., compressive and tensile) force that responds to the force applied to the substrate 102. The piezoelectric resistance sensor 112 is configured such that a change in resistance in the second piezoelectric resistance sensor 112 represents a normal force that responds to the force applied to the substrate 102. Similarly, the sensing axis 118 of the third piezoelectric resistance sensor 116 is oriented neither parallel nor perpendicular to the orientation of the crystal axis 106 (e.g., at an angle of approximately ±45° with respect to the

[0100] crystal axis). Therefore, the third piezoelectric resistance sensor 116 is configured such that a change in resistance in the third piezoelectric resistance sensor 116 corresponds to a shear force that responds to the force applied to the substrate 102.

[0037] As described above, in order for the sensing circuit 120 to be able to measure the longitudinal normal and shear forces, the orientation of the crystal axis 106 of the substrate 102 is directed parallel (or transverse) to the longitudinal axis of the mechanical structure on which the IC 100 is mounted. Thus, in order to measure the longitudinal normal force applied to the mechanical structure, the sensing axes 110, 114 of the first and second piezoresistive sensors 108, 112 are directed parallel and perpendicular to the longitudinal axis of the mechanical structure, respectively. In order to measure the shear force, the sensing axis 118 of the third piezoresistive sensor 116 is neither parallel nor perpendicular to the longitudinal axis of the mechanical structure (e.g., at an angle of about ±45° with respect to the longitudinal axis).

[0038] The first, second, and third piezoresistive sensors 108, 112, 116 are configured to exhibit a change in resistance with respect to the mechanical force along their sensing axes, but the piezoresistive sensors 108, 112, 116 also experience a change in resistance due to other forces. For example, the resistance of each of the piezoresistive sensors 108, 112, 116 responds to a force perpendicular to their respective sensing axes. In one example, each of the piezoresistive sensors 108, 112, 116 is formed on or within the substrate 102 as a plurality of piezoresistive element coupled in series between their respective terminals. For example, each of the piezoresistive elements is implemented as a doped silicon resistor (e.g., P-type or N-type) that depends on the doping of the semiconductor substrate. The plurality of piezoresistive elements includes a first (main) set of piezoresistive elements formed on the substrate having a sensing axis parallel to the desired (main) sensing axis for each of the piezoresistive sensors. For example, the main sensing axis is determined based on the longitudinal direction of the piezoresistive element with respect to the crystal axis of the semiconductor substrate. A second (e.g., compensating) set of one or more piezoresistive elements is formed on the substrate having a sensing axis transverse to the desired (main) sensing axis for each of the piezoresistive sensors 108, 112, 116. The second set of piezoresistive elements in each of the piezoresistive sensors 108, 112, 116 is configured to provide a resistance that cancels out the change in resistance due to the force perpendicular to the desired (main) sensing axis of each of the piezoresistive sensors.

[0039] As a further example, the resistances of the first and second piezoresistive sensors 108, 112 respond to shear forces applied at an angle that is neither longitudinal nor perpendicular to their respective sensing axes. Changes in the resistance of the first and second piezoresistive sensors 108, 112 due to such shear forces can skew the measured resistance of each piezoresistive sensor by introducing a change in resistance that responds to the shear force. As a result, inaccurate forces may be determined along each of the axes 110 and 114. To compensate for the resistance variations due to shear forces and to correct the final value of the measured force, the measured shear force due to the resistance of the third piezoresistive sensor 116 is used to compensate for the shear forces received by the first and second piezoresistive sensors 108, 112. Generally, when using four differently oriented resistors (examples of orientations approximately 0°, 90°, +45°, -45° with respect to the crystal axes), if normal and shear stresses are present simultaneously in different directions, the output of each sensor can be corrected for their inaccuracies by the output of the other sensors.

[0040] As an example, IC100 includes other circuit elements 123 implemented on the IC, including a controller. The controller can be implemented as a state machine, a processor core, or a microcontroller. The controller is configured to determine values representing longitudinal and perpendicular forces along axes 110, 114 in response to changes in resistance for each of the piezoresistive sensors 108, 112 (e.g., determined by the sensing circuit 120). Also, the controller is configured to determine a value representing a shear force along axis 118 in response to a change in resistance for sensor 116 (e.g., determined by the sensing circuit 120). In one example, the controller is further configured to use the shear force value (due to the third piezoresistive sensor 116) to compensate for the shear forces received by the first and second piezoresistive sensors 108, 112. As a result, the final values of the longitudinal and perpendicular forces determined by the controller in response to changes in resistance of each of the first and second piezoresistive sensors 108, 112 can be provided to be aligned with the respective sensor axes 110, 114 or to include only the force components along the sensor axes 110, 114.

[0041] Similarly, the third piezoresistive sensor 116 includes an arrangement of one or more piezoresistors having a resistance configured to vary in response to a shear force applied to the substrate 100 along the axis 118. However, the resistance of the third piezoresistive sensor 116 also varies in response to longitudinal and perpendicular forces applied to the substrate 100. The change in the resistance of the third piezoresistive sensor 116 due to the longitudinal and perpendicular forces can skew the measured resistance of each piezoresistive sensor 116 by introducing a change in its resistance in response to the longitudinal and perpendicular forces. As a result of the influence of the longitudinal and perpendicular forces on the resistance of the piezoresistive sensor 116, an inaccurate shear force may be determined along each axis 118. The longitudinal and perpendicular forces determined in response to the change in the resistance of the first and second piezoresistive sensors 108, 112 can be used to compensate for the longitudinal and perpendicular forces received by the third piezoresistive sensor 116. For example, the controller may further be configured to use the values of the longitudinal and perpendicular forces (from the piezoresistive sensors 108, 112) to compensate for the longitudinal and perpendicular forces received by the third piezoresistive sensor 116. As a result, in such an example, the final value of the shear force determined by the controller in response to the change in the resistance of the third piezoresistive sensor 116 can be determined to be aligned with each sensor axis 118 or to include only the force component along the sensor axis 118.

[0042] As a further example, still referring to the example of FIG. 1A, IC 100 includes a temperature sensor 122 formed on or within substrate surface 104. The temperature sensor has an output coupled to the input of other circuit elements 123 and is configured to provide a temperature signal representative of the temperature of substrate 102. A change in the temperature of IC 100, and thus of substrate 102, can affect the resistance of the piezoresistors in each of the respective piezoresistive sensors 108, 112, 116, which can affect the resistance values determined by sensing circuit 120. Thus, the temperature of substrate 102 is monitored, and changes in the substrate temperature are used by other circuit elements to correct the normal and shear force values measured by sensing circuit 120. Also, temperature compensation for the mismatch in the thermal expansion coefficients of the sensor substrate and the mechanical structure can be used to correct the normal and shear force values measured by circuit 120.

[0043] Also, other circuit elements 123 include an arrangement of components that depends on the functionality of IC 100. For example, the other circuit elements include inductors, capacitors, antennas, A / D converters, microcontrollers, etc. formed on mounting surface 104 of substrate 102 for implementing a system-on-chip (SoC) or the like. In one example, the SoC described in the present application is a multi-chip module (MCM). The MCM can include circuit elements / components having different technologies / functions. For example, one or more ICs of the MCM include a strain sensing sensor configured to measure strain and sensing circuit elements / components. Thus, the strain sensing IC can include analog circuit elements and components. One or more other ICs of the MCM include circuit elements (e.g., microcontrollers, state machines, processing cores) and components configured to perform processing and arithmetic operations and related control functions. The ICs in the MCM can be coupled to each other via conductive traces, wires, etc. for communicating data and instructions, for example.

[0044] In another example, some of the circuit elements 123 are implemented on a circuit board to which the IC or SoC is coupled. Also, other circuit elements 123 in the SoC (or MCM) can be configured to establish a wired or wireless link (e.g., an inductive link, near field communication (NFC), Bluetooth, etc.) for power transmission from an external circuit element to the IC 100. The other circuit elements 123 can further be used to establish a wired or wireless communication channel for communicating data between the IC and a remote system. For example, the wireless link can use the wireless communication channel to calibrate the circuit elements 120 or 123 and / or to communicate sensor readout values to an external reading system.

[0045] FIG. 1B is a block diagram of an example of a resistive stress sensing circuit element including the piezoresistive sensor 108 and the sensing circuit 120 of FIG. 1A. Accordingly, the description of FIG. 1B also refers to FIG. 1A. As shown in the example of FIG. 1B, the first piezoresistive sensor 108 includes a pair of piezoresistors 124 and 130. For example, piezoresistor 124 includes terminals 126 and 128. Terminal 128 is coupled to the output of sensing circuit 120, and terminal 126 is coupled to the first input of sensing circuit 120. Piezoresistor 130 includes terminals 132 and 134. Terminal 134 is coupled to the output of sensing circuit 120, and terminal 132 is coupled to the second input of the sensing circuit. As described in the present application, each of piezoresistors 124 and 130 can include one or more piezoresistive elements coupled between their respective terminals 126, 128 and 132, 134, and the piezoresistive elements are formed on the substrate 102 to provide sensitivity to the force applied to the substrate. For example, such sensitivity is along the sensing axis

[0110] or along another sensing axis. The output terminal 126 of the first piezoresistor 124 is coupled to the first input 136 of the sensing circuit 120, and the output terminal 132 of the second piezoresistor 130 is coupled to the second input 138 of the sensing circuit 120.

[0046] In the example of FIG. 1B, the piezoresistor 124 is a sense resistor configured to provide a variable resistance (R_SENSE) between terminals 126 and 128. For example, the resistance R_SENSE is variable in response to a longitudinal force applied to the substrate along axis 110. The piezoresistor 130 is a reference resistor configured to provide a fixed resistance (R_REF) between terminals 132 and 134. The sense circuit 120 is configured to provide first and second input signals (e.g., a DC input voltage) to respective terminals 128 and 134. For example, the first and second input signals may be the same (e.g., in this case, R_SENSE = R_REF), or the first and second input signals may be different (e.g., in this case, R_SENSE ≠ R_REF). Inputs 136 and 138 of the sense circuit 120 receive output signals from respective piezoresistors 124, 130 based on the input signals provided at 128 and 134. The sense circuit 120 is configured to provide a sense signal representative of the difference between the signals received at 136 and 138). Since the resistance R_REF of the piezoresistor 130 remains fixed, the sense signal represents the change in the resistance of the piezoresistor 124 in response to the force applied to the substrate 102. As another example, R_REF depends on a different stress compared to R_SENSE. Therefore, the sense signal (difference) also represents the change in stress. As described in the present application, the sense signal can then be used (e.g., by other circuit elements 123) to determine stress components (e.g., longitudinal, normal, and shear components) based on the change in resistance measured by the sense signal.

[0047] As a further example, the piezoresistor 124 is arranged in a lateral plane parallel to the mounting surface of the substrate 102. The piezoresistor 130 is formed on the substrate 102 having its sensitivity axis in a direction perpendicular to the lateral plane. Also, by forming each resistor to have substantially the same doping, the reference piezoresistor 130 can be configured to have the same temperature dependence as the associated sense piezoresistor 124. This configuration helps to ensure that the sense and reference piezoresistors 124 and 130 have the same temperature coefficient and respond to temperature changes in substantially the same manner, thereby improving the accuracy of the measured change in resistance with respect to temperature. In another example, different piezoresistors are combined in series, in which case each has different doping and different materials to achieve a total temperature coefficient (TC) similar to that of R_SENSE, while at the same time having different stress coefficients. In this example, the TCs cancel each other out, but the stresses do not. In yet another example, R_REF has the same doping in silicon but has a different orientation (e.g., perpendicular rather than parallel to the surface).

[0048] Each of the second and third piezoresistive sensors 112, 116 can be configured similarly to the sensor 108 to sense resistance along their respective axes 114 and 118 (in response to an applied mechanical force). Also, each of the second and third piezoresistive sensors 112, 116 can be coupled to a respective instance of the sensing circuit 120 to generate a sensing signal representative of the change in resistance of the respective piezoresistive sensors 112, 116 in response to a force applied to the substrate 102.

[0049] Figures 2A and 2B show an example of a single piezoresistor 200 that exhibits sensitivity to different mechanical stresses. The piezoresistor 200 is a useful example of a piezoresistor (e.g., the variable piezoresistor 124 in FIG. 1B) that can be implemented to form piezoresistive sensors 108, 112, and 116. In the examples of FIGS. 2A and 2B, the forces received by the piezoresistor 200 are represented only as longitudinal and transverse (e.g., normal) stresses (in the x and y directions). The exemplary single piezoresistor 200 includes resistor components shown as R1 to R5. The five resistor elements R1 to R5 are coupled in series with each other. As described in the present application, each of the resistors R1 to R5 has a first sensitivity in the longitudinal direction and a second sensitivity in the transverse direction, and the first sensitivity of each of the resistor elements is formed on a substrate with a sensitivity axis oriented with respect to the crystal axis. Therefore, the combined resistance of R1 to R5 (e.g., shown as R_SENSE in FIG. 1B) is sensitive only to one direction of stress, i.e., the longitudinal direction. Each of the resistors R1 to R4 is formed on the substrate so as to have a sensitivity axis parallel to the vertical axis. The resistor R5 is formed on the substrate so as to have a transverse (normal) sensitivity axis with respect to the vertical axis. Thus, the piezoresistor 200 is a single-direction (e.g., uniaxial) sensing resistor formed on a semiconductor substrate with a sensing axis having a specific orientation with respect to the crystal axis of the substrate.

[0050] In the examples of FIGS. 2A and 2B, the piezoresistor 200 is a longitudinal stress sensor that provides a variable resistance responsive only to longitudinal stress (σ long ) in the (y direction). The piezoresistor 200 is internally configured to cancel the effect of transverse stress (σ trans ). As an example, each of the resistor elements R1 to R4 of the piezoresistor 200 has a sensitivity to transverse stress (σ trans ) of approximately 1% / 100 MPa, which amounts to a total of 4% / 100 MPa for the combination of R1 to R4. The resistor element R5 of the piezoresistor 200 has an individual sensitivity to transverse stress (σ trans ) of approximately minus 4% / 100 MPa. For example, the following equation shows the total sensitivity to transverse (normal) stress (σ trans ) in the x direction of 0% / 100 MPa. TIFF0007705866000001.tif20136 Thus, the piezoresistor 200 has no sensitivity to transverse stress in the x direction.

[0051] As will be described, the piezoresistor 200 is configured to be sensitive to longitudinal stress (σ long ) in the y direction. R1 to R4 are formed on the substrate to provide a flow of current through the piezoresistor elements along or parallel to the y direction (e.g., the longitudinal sensing axis). In the example of FIG. 2B, the piezoresistor 200 has a pure sensitivity of -3% / 100 MPa in the longitudinal direction. For example, each resistor element R1 to R4 has an individual sensitivity of approximately minus 4% / 100 MPA to the longitudinal stress (σ long ) in the y direction. Also, the resistor element R5 of the piezoresistor 200 has an individual sensitivity to the longitudinal stress (σ long ) which is approximately plus 1% / 100 MPa. For example, the following equation shows the total sensitivity to the longitudinal (normal) stress (σ long ) in the y direction of approximately -3% / 100 MPa. TIFF0007705866000002.tif20136 Therefore, the overall sensitivity of the exemplary piezoresistor 200 to longitudinal stress is approximately -3% / 100 MPa.

[0052] In this example, the ratio of the resistor components in the y direction to the x direction is 4:1 in order to cancel out the stress in the x direction so that the piezoresistor 200 is a y-direction normal stress sensor. However, this ratio can vary based on the type of crystal substrate, the dimensions of each resistor element, the mounting orientation of the IC package, the type of application example, etc. (e.g., 1.5:1, 2:1, 3:1, 5:1, etc.). Also, in other examples, different numbers of resistor elements can be used to form the piezoresistor 200.

[0053] FIG. 3 is an example of a stress sensing circuit 300 for an IC having piezoresistive sensors configured to respond to vertical or longitudinal stress due to forces applied parallel or perpendicular to the crystal axes of a substrate. Circuit 300 includes a voltage source 301 having an output coupled to terminals 302 and 304 of first and second piezoresistors 306, 308, respectively. Each of piezoresistors 306, 308 has another terminal coupled to electrical ground. An amplifier (e.g., an operational amplifier) 310 has first and second inputs 312 and 314 and an output 316. The first input 312 is coupled to input 302 of piezoresistor 306, and the second input 314 is coupled to input 304 of piezoresistor 308. Piezoresistors 306, 308 form piezoresistive sensors for implementing piezoresistive sensors 108 and 112, etc. in IC 100 of FIG. 1.

[0054] As an example, voltage source 301 is configured to provide a DC voltage (VDD) that provides a constant current shown as 320 and 322 to each of piezoresistors 306, 308. Thus, the current through piezoresistors 306, 308 provides a voltage that varies between the piezoresistors 306, 308 based on their resistance. Amplifier 310 is configured to provide at output 316 a sense signal representative of the difference in voltage between inputs 302 and 304. For example, one of the piezoresistors 308 is configured as described with respect to FIGS. 2A and 2B to have maximum sensitivity to longitudinal stress. The other piezoresistor 306 has a fixed resistance (is not stress dependent). As described in the present application, both piezoresistors 306, 308 have the same temperature dependence. Thus, sensing circuit 300 outputs a sense signal (voltage signal) representative of the difference in resistance between first and second piezoresistors 306, 308. In one example, the sense signal at 316 is proportional to the longitudinal stress applied to piezoresistive sensor 318 including piezoresistors 306, 308.

[0055] FIG. 4 shows stress (σ long) is a graph showing the change in the resistance values of the piezoresistors 306 and 308 as it increases from 0 MPa to 100 MPa. For example, the difference in the resistance of the piezoresistors 306 and 308 changes by approximately -7% as the stress increases from 0 MPa to 100 MPa. As shown in FIG. 4, in this example, the change in resistance is linearly inversely proportional to the longitudinal stress. Also, in other examples, the change in resistance can be directly proportional based on the signs of the longitudinal and transverse stress coefficients (see FIG. 2B), which depends on the type of material, type of doping, etc. As described above, the sensing circuit 300 outputs a voltage proportional to the change in resistance in response to the longitudinal stress.

[0056] FIG. 5 is another example of a stress sensing circuit 500 for an IC having a piezoresistive sensor 502 configured to respond to shear stress (σ shear ) caused by components of a mechanical force applied parallel to the crystal axis of the substrate. Circuit 500 is the same as circuit 300 except for the orientation of each resistor element (e.g., doped silicon resistor) in piezoresistive sensor 502. Circuit 500 includes a sensing circuit element 504, and sensing circuit element 504 includes a voltage source 506 having an output coupled to terminals 508 and 510 of first and second piezoresistors 512 and 514 of piezoresistive sensor 502. Each of piezoresistors 512 and 514 has another terminal coupled to electrical ground. An amplifier 516 has first and second inputs 518 and 520 coupled to inputs 508 and 510, respectively. Also, amplifier 516 includes an output 522.

[0057] Similar to what has been described with respect to FIG. 3, the voltage source 506 is configured to provide a DC voltage (VDD) that provides constant currents shown as 524 and 526 to each of the piezoresistors 512, 514. Therefore, the currents through the piezoresistors 512, 514 produce a voltage across each of the piezoresistors 512, 514 that varies in proportion to its resistance. Different from the example of FIG. 3, each of the piezoresistors 512 and 514 is formed on the substrate with maximum sensitivity to shear stress. For example, piezoresistor 512 has an axis of maximum sensitivity oriented at approximately -45 degrees with respect to the crystal axis, and piezoresistor 514 has an axis of maximum sensitivity oriented at approximately +45 degrees with respect to the crystal axis. Thus, in this example, piezoresistors 512 and 514 are oriented (90 degrees apart) by the axes of maximum sensitivity that are orthogonal.

[0058] Amplifier 516 is configured to provide at output 522 a sense signal representative of the change in resistance between the piezoresistors 512, 514. Thus, the amplifier 516 of the sensing circuit 504 outputs a sense signal (voltage signal) representative of the difference in resistance between the first and second piezoresistors 512, 514. In one example, the sense signal at 522 is proportional to the shear stress applied to the substrate on which the piezoresistive sensor 502 is implemented.

[0059] FIG. 6 is a graph showing the change in the resistance values of the piezoresistors 512, 514 as the stress (σ shear ) increases from 0 MPa to 110 MPa. For example, the difference in resistance of the piezoresistors 512, 514 changes approximately -X as the stress increases from 0 MPa to 100 MPa. As shown in FIG. 6, in this example, the change in resistance is linearly inversely proportional to the shear stress. Also, in other examples, the change in resistance can be directly proportional based on the signs of the longitudinal and transverse stress coefficients (see FIG. 2B), which depends on the type of material, type of doping, etc. As described above, the sensing circuit 500 outputs a voltage proportional to the change in resistance in response to the shear stress.

[0060] FIG. 7 and FIG. 8 illustrate examples of SoCs 700, 800 that can be implemented using IC 100 to provide respective stress sensing systems. The SoC is adapted to be coupled to a mechanical structure to measure mechanical stress in the structure, including normal stress and shear stress (in one or more directions). As described herein, the IC includes a substrate 102 integrated with piezoresistive sensors (e.g., sensors 108, 112, 116) formed on or within the substrate surface. The piezoresistive sensors are configured to change resistance in response to a force applied to the IC 100. Also, the IC 100 includes circuit elements (e.g., sensing circuit 120) configured to measure a change in resistance (e.g., proportional thereto) representative of a stress component (e.g., normal and / or shear stress). In another example, the SoCs 700, 800 are implemented as a multi-chip module (MCM) that includes a plurality of ICs (including one or more examples of the IC 100) configured to perform respective functions as described herein.

[0061] In the example of FIG. 7, the SoC 700 includes other components and / or circuit elements 702 coupled to the IC 100. The SoC 700 includes a packaging material (e.g., epoxy molding compound, magnetic molding compound, polyimide, metal, plastic, glass, ceramic, etc.) 704 that encapsulates the IC 100 and the components / circuit elements 702 mounted therein. The other components and / or circuit elements 702 may include inductors, capacitors, antennas, A / D converters, microcontrollers, and the like. The other components and / or circuit elements 702 are integrated with a part of the substrate 102 and the IC, or are mounted on the mounting surface 706 of the substrate 102 via interconnections (e.g., solder bumps) 708. In the example of FIG. 7, an antenna 710 is shown as being mounted on the mounting surface 706 of the substrate 102. Alternatively, the antenna 710 can be an external antenna. For example, the SoC 700 may include one or more pins 712 configured to couple such an external (or other external component) to the substrate 102. Thus, the other components / circuit elements can be inside the package 700 or outside and connected via a set of pins coupled to the internal circuit elements and / or components. The pins 712 can provide communication to and from external components (e.g., signal readout, analog / digital signals, sensing signals, etc.). The SoC 700 may include a coupling layer (e.g., a metal layer including a lead frame, etc.) 714 that is attached to the contact surface of the IC (the surface opposite the mounting surface 706) for attaching the SoC 700 to each surface 716 of the mechanical structure 718. Alternatively, the coupling layer 714 can be omitted and the contact surface of the substrate 102 is directly mounted on the processed surface 716 of the mechanical structure 718.

[0062] FIG. 8 is another example of the SoC 800 including the IC 100 having the monolithic single-crystalline substrate 102 as described above. The SoC 800 includes similar components to the SoC 700 of FIG. 7. Therefore, the description of FIG. 8 also refers to FIG. 7. Further, the SoC 800 includes an interposer layer (e.g., a printed circuit board (PCB)) 802 mounted on the mounting surface 706 of the substrate 102 via the interconnect 708. The other components / circuit elements 702 and the antenna 710 are mounted on the interposer (PCB) 802 and coupled to the substrate 102 via the interconnects formed on the interposer 802. In another example, the other components / circuit elements 702 and the antenna 710 can be additional PCB substrates with their own functions integrated into one package together with the interposer 802.

[0063] As a further example, FIGS. 9-13 illustrate exemplary mounting orientations for the SoC 900. The SoC 900 can be implemented by the SoC 700, 800 and includes the IC 100 as described above. FIG. 9 illustrates the SoC 900 mounted on the surface of a mechanical structure (e.g., a shaft, a beam, a feather key, etc.) 902. In one example, two or more SoCs may be mounted on the mechanical structure 902. Alternatively, as described in the present application, the IC 100 itself can be used as an SoC and directly mounted on the mechanical structure 902. The SoC or the IC can be coupled to the mechanical structure 902 via an adhesive, a clamp, a metal joint, a feather key.

[0064] Figures 10-13 illustrate the orientation of an exemplary SoC900 (or IC100) having an arrangement of piezoresistive sensors when coupled to a mechanical structure to measure mechanical stress of the mechanical structure as described in the present application. In the examples of Figures 10-13, the piezoresistive sensors mounted on the IC100 each have a sensing axis having a respective orientation with respect to the crystal axes of the semiconductor substrate 102. In another example, the arrangement of the piezoresistive sensors can be mounted on the IC100 such that the respective sensing axes of the piezoresistive sensors are oriented with respect to the crystal axes of a wafer cut in respective different crystal planes (e.g., cut in

[0100] ,

[0110] ,

[0111] or other crystal planes). Thus, in accordance with the orientation of the crystal axes of the substrate, the IC100 and the SoC900 can be coupled to the mechanical structure in an orientation to align the maximum sensitivity axes of the respective piezoresistive sensors with the force components to be measured on the mechanical structure 902. For example, each of the normal and shear piezoresistive sensors is aligned to measure the longitudinal, normal, and shear forces applied to or received by the mechanical structure. An alignment mark can be printed on the IC100 or the SoC to indicate, for example, the direction of longitudinal sensing (parallel to the crystal axes of the substrate 102). In another example, the SoC900 is implemented as a multi-chip module (MCM) including a plurality of ICs (including one or more examples of the IC100) configured to perform respective functions as described in the present application.

[0065] Figures 10 and 11 illustrate an exemplary IC (or SoC) 1000 coupled to the surface of a mechanical structure 1002. In the examples of Figures 10 and 11, the IC1000 includes piezoresistive sensors 1004, 1006, and 1008 formed on a

[0100] semiconductor substrate having a crystal axis extending through the IC, indicated by 1010. For example, the piezoresistive sensors 1004, 1006, and 1008 can be implemented by piezoresistive sensors 108, 112, 116, each including a respective pair of piezoresistors as described in the present application.

[0066] FIG. 10 shows the orientations of the normal piezoresistive sensors 1004 and 1006 each having respective longitudinal sensing axes 1012 and 1014 in the x - direction and y - direction respectively. For example, the piezoresistive sensor 1004 (having variable resistor R 0° ) is an x - direction normal stress sensor having a longitudinal sensing axis oriented parallel to the x - direction parallel to the axis 1010. The other normal piezoresistive sensor 1006 (having variable resistor R 90° ) is a y - normal stress sensor having a longitudinal sensing axis oriented parallel to the y - direction perpendicular to the axis 1010.

[0067] FIG. 11 separately shows the piezoresistive sensor 1008 as including two piezoresistors shown as R 45° , R -45° . The piezoresistive sensor 1008 is a shear stress sensor having a sensing axis 1016 that is oriented neither parallel nor perpendicular to the axis 1010. In one example, the piezoresistive sensor 1008 includes piezoresistors shown as R 45° , R -45° which are oriented at approximately + 45° and - 45° with respect to the axis 1010 (in the x - direction) of the substrate of the IC1000.

[0068] In the examples of FIGS. 10 and 11, the axis 1010 of the substrate of the IC1000 is parallel to the longitudinal axis 1018 of the mechanical structure 1002. Therefore, the sensing axis 1012 of the piezoresistor 1004 is parallel to the longitudinal axis 1018 of the mechanical structure 1002, the sensing axis 1014 of the piezoresistor 1006 is perpendicular to the longitudinal axis 1018 of the mechanical structure 1002. Also, the sensing axis 1016 of the piezoresistive sensor 1008 is oriented at ± 45° with respect to the longitudinal axis 1018 of the mechanical structure 1002. The piezoresistors 1004, 1006 having sensing axes 1012, 1014 that are parallel and perpendicular respectively to the longitudinal axis 1018 of the mechanical structure 1002 are configured to measure normal forces along the surface of the mechanical structure. The piezoresistive sensor 1008 is configured to measure shear forces along the surface of the mechanical structure.

[0069] Figures 12 and 13 illustrate an exemplary IC (or SoC) 1200 coupled to the surface of a mechanical structure 1202. In the example of FIGS. 12 and 13, the IC 1200 includes piezoresistive sensors 1204, 1206, and 1208 formed on a

[0110] semiconductor substrate having a

[0100] crystal axis extending therethrough as shown at 1210. For example, piezoresistive sensors 1204, 1206, and 1208 may be implemented by piezoresistive sensors 108, 112, 116, each of which includes a respective pair of piezoresistors as described herein.

[0070] FIG. 12 shows the orientation of normal piezoresistive sensors 1204 and 1206 having respective longitudinal sensing axes 1212 and 1214 offset approximately 45° from the substrate orientation (substrate axis) 1210 as shown. For example, piezoresistive sensor 1204 (having variable resistor R -45° ), is oriented at -45° with respect to the substrate orientation, has a longitudinal sensing axis 1212 along

[0100] of the substrate and parallel to axis 1210. Thus, piezoresistive sensor 1204 is configured to sense stress in a direction parallel to axis 1218 of mechanical structure 1202. The other normal piezoresistive sensor 1206 (having variable resistor R 45° ) is a y-normal stress sensor oriented at +45° with respect to the crystal axis, having a longitudinal sensing axis 1214 along

[0010] of the crystal and perpendicular to axis 1210. Thus, piezoresistive sensor 1206 is configured to sense normal stress in a direction perpendicular to axis 1218 of the mechanical structure.

[0071] FIG. 13 separately shows piezoresistive sensor 1208 as including two piezoresistors shown as R 90° , R 0° . Piezoresistive sensor 1208 is a shear stress sensor having resistors parallel and perpendicular to the substrate orientation and oriented at + / -45° with respect to axis 1210. In one example, piezoresistive sensor 1208 has R 0° , R 90°including piezoresistors shown as such, which are oriented at approximately 45° and -45° with respect to axis 1210, i.e., along

[0110] and [-110] of the substrate of IC1200.

[0072] In the examples of FIGS. 12 and 13, the axis 1210 of the substrate for sensors 1204, 1206 is aligned parallel to the longitudinal axis 1218 of the mechanical structure 1202 by rotating the IC1200 by 45° (compared to FIGS. 10 and 11) as shown. As a result of the rotation of the IC1200, the sensing axis 1212 of the piezoresistor 1204 becomes parallel to the longitudinal axis 1218 of the mechanical structure 1202, and the sensing axis 1214 of the piezoresistor 1206 becomes perpendicular to the longitudinal axis 1218 of the mechanical structure 1202. Also, the sensing axis 1216 of the piezoresistive sensor 1208 is oriented at ±45° with respect to the longitudinal axis 1218 of the mechanical structure 1202. Thus, the piezoresistors 1204, 1206 are configured to measure the normal force along the surface of the mechanical structure. The piezoresistive sensor 1208 is configured to measure the shear force along the surface of the mechanical structure 1202.

[0073] FIGS. 14 - 18 illustrate another exemplary mounting orientation for the SoC1400. The SoC1400 can be implemented according to the exemplary SoC700, 800 of FIGS. 7 and 8 as described above, each including an IC100. FIG. 14 illustrates the SoC1400 mounted in a notch or slit 1402 perpendicular to the surface of a mechanical structure 1404 (e.g., a shaft, a beam, etc.). In another example, the SoC1400 is mounted on the sidewall of a carrier material (e.g., on the side of a feather key structure) that can be mounted in a keyway or a recess.

[0074] Figures 14 to 18 illustrate the orientation of the SoC and each piezoresistive sensor with respect to the mechanical structure for measuring the longitudinal direction, normal, and shear mechanical forces. As described in the present application, the piezoresistive sensors mounted on the IC100 each have a sensing axis with a respective orientation with respect to the crystal axis of the semiconductor substrate 102. Therefore, according to the orientation of the crystal axis of the substrate, the IC100 and the SoC1400 can be coupled to the mechanical structure 1404 in an orientation for aligning the highest sensitivity axes of the respective piezoresistive sensors with the force components to be measured on the mechanical structure 1404. For example, each of the normal and shear piezoresistive sensors is aligned to measure the longitudinal, normal, and shear forces applied to the mechanical structure 1404 or received by the mechanical structure 1404. An alignment mark can be printed on the IC100 or the SoC to indicate, for example, the direction of longitudinal sensing (e.g., parallel to the crystal axis of the substrate 102). In one example, the SoC of FIGS. 14 to 18 is implemented as a MCM including a plurality of ICs (including one or more strain sensing ICs) configured to perform their respective functions as described, for example, in the present application.

[0075] FIGS. 15 and 16 illustrate an exemplary IC (or SoC) 1500 coupled in the slot 1501 of the mechanical structure 1502. The IC1500 includes piezoresistive sensors 1504, 1506, and 1508 formed on a

[0100] semiconductor substrate having a crystal axis extending through the SoC, indicated at 1510. For example, the piezoresistive sensors 1504, 1506, and 1508 can be implemented by piezoresistive sensors 108, 112, 116, each of which includes a respective pair of piezoresistors as described in the present application.

[0076] FIG. 15 shows the orientation of the normal piezoresistive sensors 1504 and 1506 having respective longitudinal sensing axes 1512 and 1514 in the x and y directions, respectively. For example, the piezoresistive sensor 1504 (having a variable resistance R 0° ) is an x-normal stress sensor having a longitudinal sensing axis oriented parallel to the x direction parallel to the axis 1510. The other (variable resistance R 90°The normal piezoresistive sensor 1506 has a longitudinal sensing axis oriented parallel to the y direction perpendicular to the axis 1510 and is a y-normal stress sensor.

[0077] FIG. 16 separately shows the piezoresistive sensor 1508 as including two piezoresistors shown as R 45° , R -45° . The piezoresistive sensor 1508 is a shear stress sensor having a sensing axis 1516 that is neither parallel nor perpendicular to the axis 1510. In one example, the piezoresistive sensor 1508 includes piezoresistors shown as R 45° , R -45° and is oriented approximately +45° and -45° with respect to the axis 1510 (in the x direction) of the substrate of the IC 1500.

[0078] In the examples of FIGS. 15 and 16, the axis 1510 of the substrate of the IC 1500 is parallel to the longitudinal axis 1518 of the mechanical structure 1502. Therefore, the sensing axis 1512 of the piezoresistor 1504 is parallel to the longitudinal axis 1518 of the mechanical structure 1502, the sensing axis 1514 of the piezoresistor 1506 is perpendicular to the longitudinal axis 1518 of the mechanical structure 1502, and the sensing axis 1516 of the piezoresistive sensor 1508 is oriented at ±45° with respect to the longitudinal axis 1518 of the mechanical structure 1502. Thus, the piezoresistors 1504, 1506 are configured to measure normal forces, and the piezoresistive sensor 1508 is configured to measure shear forces along the mechanical structure in the substrate. This respectively leads to measuring the torque and bending of the mechanical structure.

[0079] Figures 17 and 18 illustrate an exemplary IC (SoC) 1700 coupled in the slot 1701 of the mechanical structure 1702. In the examples of FIGS. 17 and 18, the IC 1700 includes piezoresistive sensors 1704, 1706, and 1708 formed on a

[0110] semiconductor substrate having a crystal axis extending through the IC 1700, indicated at 1710. For example, piezoresistive sensors 1704, 1706, and 1708 may be implemented by piezoresistive sensors 108, 112, 116, each of which includes a respective pair of piezoresistors as described herein.

[0080] FIG. 17 shows the orientation of the normal piezoresistive sensors 1704 and 1706 having respective longitudinal sensing axes 1712 and 1714 offset approximately 45° from the substrate orientation 1710 as shown. For example, the piezoresistive sensor 1704 (having variable resistor R- 45° ) has a longitudinal sensing axis 1712 that is along the

[0100] of the crystal and is oriented -45° with respect to the substrate orientation parallel to the axis 1710. Thus, the piezoresistive sensor 1704 is configured to sense the normal stress in the substrate that represents torque and / or bending in the mechanical structure 1702. The other normal piezoresistive sensor 1706 (having variable resistor R 45° ) is a y normal stress sensor having a longitudinal sensing axis 1714 that is oriented +45° with respect to the substrate orientation (along the

[0010] of the crystal) perpendicular to the axis 1710. Thus, the piezoresistive sensor 1706 is configured to sense the normal stress in a direction perpendicular to the axis 1718 of the mechanical structure 1702.

[0081] FIG. 18 shows R 90° 、R 0°The piezoresistive sensor 1708 is shown separately as including two piezoresistors shown as such. The piezoresistive sensor 1708 is a shear stress sensor having resistors that are parallel and perpendicular to the substrate orientation and are oriented at + / -45° with respect to the axis 1710. In one example, the piezoresistive sensor 1708 is oriented approximately 90° and 0° with respect to the substrate orientation, and + / -45° with respect to the axis 1710, that is, along the

[0010] and

[0100] of the substrate of the IC1700, R 0° , R 90° and includes the piezoresistors shown as such.

[0082] In the examples of FIGS. 17 and 18, the crystal axis 1710 on the substrate of the IC1700 is aligned parallel to the longitudinal axis 1718 of the mechanical structure 1702 by rotating the IC1700 by 45° as shown (compared with FIGS. 15 and 16). As a result of the rotation of the IC1700, the sensing axis 1712 of the piezoresistor 1704 becomes parallel to the longitudinal axis 1718 of the mechanical structure 1702, and the sensing axis 1714 of the piezoresistor 1706 becomes perpendicular to the longitudinal axis 1718 of the mechanical structure 1702. Also, the sensing axis 1716 of the piezoresistive sensor 1708 is oriented at ±45° with respect to the longitudinal axis 1718 of the mechanical structure 1702. In this way, the piezoresistors 1704, 1706 are configured to measure the normal force, and the piezoresistive sensor 1708 is configured to measure the shear force along the mechanical structure 1702.

[0083] FIG. 19 illustrates an exemplary stress sensing system 1900 including the IC1902. In one example, the IC1902 includes a substrate and piezoresistive sensor arrangements such as the sensors 108, 112, 116, etc. or in other ways described in the present application. The IC1902 can be configured to measure stress along a plurality of directions, including normal stress and shear stress along the vertical sensing axis. Therefore, the stress sensing system 1900 can be called a torque sensor system.

[0084] In the example of FIG. 19, the torque sensor system 1900 includes a printed circuit board (PCB) 1904 coupled to the mounting surface 1906 of the IC 1902 via an interconnection (e.g., a solder ball) 1908. The torque sensor system 1900 may include a coupling (metal) layer 1910 coupled to the contact surface 1912 of the IC 1902, and the coupling layer 1910 is adapted to be coupled to a mechanical structure. Alternatively, the contact surface 1912 may be adapted to be directly attached to the mechanical structure by an adhesive, a clamp, a metal joint, a shaft joint, etc. A communication device (e.g., a transponder coil) 1914 is attached to the opposite side of the PCB 1904 and is configured to provide a wireless interface for transmitting power and data between the IC 1902 and external electronic circuit elements. Also, the system 1900 may include a microcontroller (e.g., one or more of a microprocessor, a digital signal processor, an FPGA, etc.) 1916 attached to the opposite side of the PCB 1904. For example, the microcontroller is configured to function as a readout circuit for converting the measured change in resistance (from a piezoresistive sensor) into respective stress and / or torque measurements. Further, the microcontroller 1916 may process signals from the IC, for example, to implement additional temperature compensation or to determine the situation of the mechanical structure to which the system 1900 is coupled. Also, the microcontroller 1916 may control the communication device 1914 to communicate sensor data, etc. between the IC 1902 and external circuit elements, for example, via a wire or via a wireless communication protocol (e.g., NFC, ZigBee, Bluetooth, etc.).

[0085] Figures 20 and 21 illustrate an exemplary application of the torque sensor system 1900 of FIG. 19 coupled to a mechanical structure 2000. The mechanical structure 2000 includes a fixed support 2002 fixed at one end and a flexible support 2004 at the opposite end. In some alternative examples, both ends of the mechanical structure 2000 are fixed. The metal beam cantilever 2006 has a fixed end 2008 fixed to the fixed support 2002 and a movable end 2010 disposed on the flexible support 2004. Alternatively, the metal beam 2006 may be fixed along the side surface of the mechanical structure 2000. The torque sensor system 1900 is coupled to the surface of the metal beam cantilever 2006 via a coupling layer 1910 as described in this application. The IC 1902 is placed on the cantilever surface near the fixed end 2002 of the cantilever 2006. In some examples, when a normal force NF is applied to the mechanical structure 2000, the movable end 2010 of the metal beam cantilever 2006 is deflected as shown in FIG. 21. This deflection bends the metal beam cantilever 2006, thereby applying stress to the contact surface of the IC 1902 of the torque sensor system 1900 in response to this bending. As described above, the stress can be determined by measuring the change in the resistance of the piezoresistors implemented on the IC 1902 of the torque sensor system 1900.

[0086] Figures 22, 23, and 24 illustrate another exemplary application of the torque sensor system 1900 of FIG. 19 coupled to another mechanical structure 2200. As shown in FIGS. 22 and 23, the torque sensor system 1900 is mounted in a notch area 2202 of the mechanical structure 2200 and is oriented to detect stress along respective sensing axes (see, e.g., FIGS. 14-18). The mechanical structure 2200 includes a movable shaft 2204, a fixed support 2206 at one end, and a flexible support 2208 at the opposite end. A metal beam cantilever 2210 has a fixed end 2212 fixed to the fixed support 2206 and another end 2214 disposed on the flexible support 2208 movable in response to torque applied to the shaft 2204. The torque sensor system 1900 is coupled to the metal beam cantilever 2210 via a coupling layer 1910. As shown in FIG. 23, when a torque force TF (see FIG. 23) is applied to the mechanical structure 2200, the torque force twists the shaft 2204 about its longitudinal axis. When the sensor torque system 1900 is installed to extend along the radial direction of the shaft 2204 (see, e.g., FIG. 14), the torque is converted into respective stress components similar to the stress on the metal beam cantilever in the examples of FIGS. 20 and 21. For example, in response to the torque force TF, the end 2214 of the metal beam cantilever 2210 deflects, which bends the metal beam cantilever 2216, thereby applying stress on the surface of the IC substrate coupled to the cantilever. As described above, the stress can be determined by measuring a change in the resistance of the piezoresistors mounted on the IC 1902 in the torque sensor system 1900.

[0087] FIG. 24 illustrates an example of wireless communication between the torque sensor system 1900 and an external system. For example, a transmitter coil (e.g., an antenna) 2216 is wound around the housing 2218 of the movable shaft 2204. Thus, the housing 2218 remains stationary with respect to the force applied to the movable shaft 2204 as compared to the movable shaft 2204. An electric field 2220 is generated by a communication device (e.g., a transponder coil) 1914, and the electric field 2220 transmits a data signal 2222 to the transmitter coil 2216, and the transmitter coil 2216 communicates with an external reading system. Also, an external circuit element may be configured to provide a wireless power signal that can be provided to the transmitter coil 2216 and received by the communication device 1914. The received power signal can be collected, for example, by converting it into electrical energy for storage in a battery (or other energy storage element) mounted on the PCB 1904. Alternatively, the communication device (e.g., a transponder coil) 1914 may be wound around the movable shaft 2204, and the transmitter coil 2216 may be placed on the shaft housing 2218. In yet another configuration, the communication device (e.g., a transponder coil) 1914 may be wound around the movable shaft 2204, and the transmitter coil 2216 may be wound around the shaft housing 2218. Also, the wireless communication system may include a plurality of antennas (e.g., four transmitter antennas placed stationary at an azimuth of 90° with respect to the shaft axis on the shaft housing and one transponder antenna rotating freely on the shaft, or vice versa). Furthermore, there may be a plurality of transmitter and transponder antennas placed on the shaft inside the housing. The antennas do not need to be wound completely around the shaft or the shaft housing.

[0088] FIGS. 25 and 26 illustrate another exemplary torque sensor system 2500 that includes an IC such as IC 100 described in the present application. The torque sensor system 2500 includes a substrate 2502 having a sensor area 2504, and the sensor area 2504 includes an arrangement of piezoresistive sensors as described in the present application. In the example of FIGS. 25 and 26, the substrate 2502 (e.g., a monolithic single crystal substrate) functions as a carrier (i.e., the metal beam in the above example) in the mechanical structure. Also, the system 2500 may include a printed circuit board (PCB) 2506 attached to the mounting surface 2508 of the substrate 2502 via an interconnection (e.g., a ball bond) 2510. To maintain a uniform height of the PCB 2506 with respect to the surface of the substrate 2502, polymer pillars 2512 are provided between the PCB 2506 and the substrate 2502. A coupling layer (e.g., a lead frame) 2514 is attached to the contact surface 2516 of the substrate 2502. The coupling layer 2514 couples the substrate 2502 to the mechanical structure. In the example of FIGS. 25 and 26, a communication device (e.g., a transponder / power coil) 2518 is coupled to the opposite side of the PCB 2506 and provides an interface for transmitting power and / or data between the system 2500 and external circuit elements. Also, a microcontroller 2520 may be coupled to the opposite side of the PCB 2506. As described, the microcontroller may be configured to further process the sensed signal, to function as a readout circuit, and / or to control communication between the system 2500 and external circuit elements via a wireless protocol. In another example, some or all of the circuit elements coupled to the PCB 2506 may be implemented in an IC or otherwise coupled to the IC in a system-on-chip (SoC).

[0089] FIG. 27 illustrates an exemplary application of the torque sensor system 2500 of FIG. 25 coupled to a mechanical structure 2700. The mechanical structure 2700 includes a housing 2702. The housing 2702 includes a fixed support 2706 fixed to one end of the housing 2702, and the fixed support 2706 fixes the coupling layer 2514 and one end of the substrate 2502. Also, the housing 2702 includes a non-fixed support 2708 at the opposite end of the housing 2702. The coupling layer 2514 and the opposite end of the substrate 2502 are disposed within the non-fixed support 2708. The non-fixed support 2708 allows movement of the carrier (i.e., the substrate 2502) in the thrust direction TD, rather than in a direction perpendicular to the plane of the substrate 2502. Thus, the torque sensor 2500 can be configured to measure stress in response to any force that displaces the substrate 2502 in the thrust direction.

[0090] FIG. 28 is a cross-sectional view of an exemplary reference piezoresistor 2800. The piezoresistor 2800 is a useful example of the reference piezoresistor 130 shown in FIG. 1B. The piezoresistor 2800 can be an n-type resistor, or alternatively a p-type resistor, depending on the type of dopant used to form the semiconductor substrate. A deep well 2801 is implanted into the doped substrate 2802 with a dopant of the opposite conductivity type. The substrate 2802 can include an epitaxial layer (not particularly shown). The deep well 2801 forms an embedded layer and is highly doped to promote the flow of current and exhibit low resistance. The trench 2804 is a deep trench with doped sidewalls that contacts both ends of the deep well 2801, is highly doped for horizontal current flow, and is lightly doped for vertical current flow. Thereby, the trench 2804 has a first piezoresistive coefficient for horizontal current flow and a second, even higher piezoresistive coefficient for vertical current flow.

[0091] Referring further to FIG. 28, well 2806 is implanted into the surface of substrate 2802 so as to contact trench 2804, and then implantation of a second, oppositely conductive well 2808 follows. Thereafter, dielectric layer 2810 is formed to cover the surface of substrate 2802. Contact 2812 having a first conductivity type (e.g., N-type) is implanted into well 2806 (e.g., an N-well), and contact 2814 having a second, oppositely conductivity (e.g., P-type) is implanted into well 2808 having the second conductivity. Intermediate dielectric layer 2816 is deposited over dielectric layer 2810, and via 2818 is formed through intermediate dielectric layer 2816 to contacts 2812 and 2814. Metallization layer 2820 is formed over via 2818. During operation, as shown in FIG. 28, current 2822 flows upward from one well 2806, through trench 2804 and deep well 2801 and through the other well 2806.

[0092] FIG. 29 is a cross-sectional view of an exemplary sense piezoresistor 2900. Piezoresistor 2900 is a useful example of a resistor element of the sense piezoresistor 124 shown in FIG. 1B. For example, one or more sense piezoresistors 2900 can be used to implement sense piezoresistor 124 and can be combined with piezoresistor 2800 to form a piezoresistive sensor.

[0093] In the example of FIG. 29, the sensing piezoresistor 2900 is formed on a substrate 2801 (e.g., on the same substrate as piezoresistor 2800). The sensing piezoresistor 2900 may be formed as a P-type or N-type diffused resistor on the top surface of the substrate and may be oriented along a particular crystal axis (e.g., may be oriented along

[0100] ,

[0010] , or

[0110] ). The buried layer 2904 is formed on or within the substrate 2801. For example, the buried layer 2904 is formed by implanting a dopant of a first conductivity type (e.g., an N-type or P-type dopant). The epitaxial layer 2906 is formed on the buried layer 2904. Another buried layer 2908 is formed within the epitaxial layer 2906. For example, the buried layer 2908 is formed by implanting a dopant having a conductivity type opposite to that of the buried layer 2904. The doped well region 2910 is formed within the buried layer 2908 by implanting a dopant such as one having the same conductivity type as the buried layer 2908 formed therein. An additional doped well region 2912 is formed on the opposite side of the well region 2910. This well region is formed by implanting a dopant having a conductivity opposite to that of the well region 2910, thus forming respective junctions between each of the well regions 2912 and 2910. For example, an N-type piezoresistor may be formed by implanting an N-type dopant to form well 2912 and a P-type dopant for well 2910.

[0094] A shallow trench isolation structure 2914 may be formed around the well region 2912. A dielectric layer 2916 including respective n-contacts 2918 is formed on the well region 2912. A via 2920 is formed through the dielectric layer 2916 to each of the contacts 2918. A metallization layer 2922 is formed on the via 2920. A current 2924 flows from the n-contact 2918 at one end of the dielectric layer 2916, along the junction between layers 2910 and 2912, to the other n-contact 2918 at the opposite end of the piezoresistor 2900.

[0095] In the examples described in this application, a normal piezoresistive sensor (e.g., sensor 108 and / or 112) includes an arrangement of sensing resistor 2900 formed on a lateral plane parallel to the mounting surface of substrate 2801. The resistance from the sensing resistor is compared to the resistance from a reference resistor 2800 in a direction perpendicular to the lateral plane. The reference resistor may have the same temperature dependence as the associated sensing resistor 2900 by forming the reference resistor in the same substrate as the sensing resistor with substantially the same doping concentration. This ensures that the sensing and reference resistors have the same temperature coefficient and respond to temperature changes in substantially the same way, preventing confusion of different temperature responses to an actual stress on the sensing resistor.

[0096] FIG. 30 is a perspective view of an exemplary mounting assembly 3000 that includes an IC 3002 attached to a surface 3004 of a mechanical structure (e.g., a shaft, a beam, etc.) 3006. IC 3002 includes a substrate 3008 and an arrangement of piezoresistive sensors such as sensors 108, 112, 116, etc. or other ways described in this application disposed on a mounting surface 3010 of substrate 3008. An interconnect 3012 is disposed between a contact surface of substrate 3008 (the surface opposite mounting surface 3010) and surface 3004 of mechanical structure 3006. To improve the interconnect between IC 3002 and mechanical structure 3006, one or both surfaces may be processed via machining prior to the placement of interconnect 3012. The type of processing used to treat each surface may vary depending on the material properties of the surface and the form of the adhesive interconnect 3012. Processing techniques may include texturing, patterning, cleaning, stripping, etc., or any combination thereof.

[0097] An example of the interconnection 3012 between the substrate 3008 and the mechanical structure 3006 is an adhesive interconnection. The adhesive interconnection is an interconnection between two materials (e.g., metals), and the two materials essentially become one integrated joint. Examples of some different types of adhesive interconnections 3012 include adhesives (e.g., epoxy), nanowires, welding (e.g., those formed by a welding process such as spot welding, ultrasonic welding, or laser welding), and sintering (e.g., copper or silver sintering).

[0098] Another example of the interconnection 3012 includes a form fit interconnection, in which case the connection of two connecting members creates a push-in connection. The form fit connection has strict tolerances and there is no risk of the connecting members coming loose. Examples of form fit interconnections include screws, clamps, press-fit hooks / bolts, and snap fits.

[0099] Yet another example of the interconnection 3012 includes a traction or friction connection, in which case the static friction between the adjacent surfaces of two connecting members prevents movement between the two connecting members. For example, the relative displacement of the two connecting members is prevented unless the opposing force generated by the static friction between the connecting members is exceeded.

[0100] Some examples of the above mounting methods may include silicon-metal (e.g., steel) bonding by induction heating. In the case of induction heating, the interconnection 3012 may include solder applied to the contact surface of the substrate and / or the processed surface of the mechanical structure. Heat is generated in an insulated area several micrometers below the surface of the mechanical structure. Then, a bond is formed by a low-temperature eutectic solder with an adhesive layer of, for example, gold, silver, or nickel.

[0101] Another example includes laser micro-welding, for example, in which case the lead frame of an IC is welded to a mechanical structure (e.g., a stainless steel shaft). In this example, the IC may be partially encapsulated by a material that can be welded to the mechanical structure, or may have a coupling layer (e.g., a metal base layer) that can be welded to the mechanical structure to form the interconnection 3012.

[0102] Yet another example of the interconnect 3012 involves plastic deformation and cold metal welding of flat (e.g., unpatterned) or patterned metal. In this example, both the contact surface of the substrate (or coupling layer) and the processed surface of the mechanical structure are patterned to enhance the bond. More specifically, a sealing ring is patterned on both the contact surface and the processed surface. When attached, the metal rings overlap and undergo plastic deformation. The metal rings can be cold welded to create an intermetallic bond and a seal between the respective parts.

[0103] Another example of the interconnect 3012 involves ultrasonic welding, in which high-frequency ultrasonic acoustic vibrations are applied locally to the workpiece, and the workpiece is pressed together to form a solid weld. This is generally used for plastics and metals, especially for joining dissimilar materials. In ultrasonic welding, there are no connecting bolts, nails, solder materials, or adhesives required to bond the materials to each other. When applied to metals, a notable characteristic of ultrasonic welding is that the temperature remains well below the melting points of the materials involved, thus preventing undesirable characteristics or reactions that could result from high-temperature exposure of such materials.

[0104] For each of the exemplary interconnects 3012 described herein, when attaching an IC to a mechanical structure, the physical (e.g., electrical, mechanical, and / or thermal) characteristics of the interconnect between adjacent surfaces (i.e., the contact surface of the substrate and the processed surface of the mechanical structure) can be configured based on the application example of the IC sensor. For example, with respect to mechanical characteristics, the mechanical connection between the bonding surfaces can be configured as a stronger or weaker connection based on the application example. A strong joint connection improves the sensitivity of the sensor by transmitting more stress from the surface of the mechanical structure to the sensor. As a result, in application examples where sensitivity is important, a stronger mechanical connection can increase the transmission of stress. Conversely, a weaker mechanical connection can reduce the amount of stress transmission to the sensor, resulting in a decrease in the sensitivity of the sensor.

[0105] Also, the mechanical properties of the interconnect 3012 can be configured to be isotropic or anisotropic. In the case of an example of an anisotropic interconnect, the interconnect 3012 is configured to transmit stress to the sensor along one or more specific directions, such that the sensor is more sensitive to the stress in each direction relative to other directions. In contrast, an isotropic interconnect 3012 can transmit stress from all directions uniformly from the mechanical structure to the sensor.

[0106] Also, the electrical properties of the interconnect 3012 can be configurable. For example, the interconnect can be formed from a conductive material, an electrically insulating material, or can have a resistivity or permittivity configured based on the application example.

[0107] Also, the thermal properties of the interconnect 3012 can be configurable. For example, the interconnect can be formed from a material having a thermal conductivity for controlling heat transfer between two joining surfaces. The interconnect 3012 can have a high thermal conductivity in application examples where it is desirable to expose the IC to the temperature of the mechanical structure (e.g., when the IC or SoC also includes a temperature sensor). Conversely, the interconnect 3012 can be formed from a material having a low thermal conductivity in application examples where it is desirable to isolate the sensor from the temperature of the mechanical structure to which the sensor is attached. In addition to the thermal conductivity, the interconnect 3012, the substrate, and the mechanical structure can be formed from materials having the same or similar coefficients of thermal expansion. This ensures that the substrate, and thus the IC, expands and contracts at a similar rate as the mechanical structure.

[0108] In this application example, the term "coupled" means an indirect or direct connection. Thus, when a first device is coupled to a second device, such a connection can be through a direct connection or through an indirect connection via other devices and connections. For example, when device A generates a signal for controlling device B to perform a certain action, in a first example device A is coupled to device B, or in a second example, device A is coupled to device B via intervening component C when intervening component C does not substantially change the functional relationship between device A and device B, and device B is controlled by device A via the control signal generated by device A.

[0109] In this description, the description "based on" means "at least partially based on". Thus, when X is based on Y, X can be a function of Y and any number of other factors.

[0110] Within the scope of the claims, modifications to the described embodiments are possible and other embodiments are possible.

Claims

1. An integrated circuit (IC) comprising: a semiconductor substrate; a first piezoresistive sensor on or within the semiconductor substrate, having a first sensing axis extending in a first direction parallel to the surface of the semiconductor substrate, and including a first silicon resistor and a second silicon resistor; a second piezoresistive sensor on or within the semiconductor substrate, having a second sensing axis extending in a second direction parallel to the surface of the semiconductor substrate and perpendicular to the first direction, and including a first silicon resistor and a second silicon resistor; a third piezoresistive sensor on or within the semiconductor substrate, having a third sensing axis extending in a third direction parallel to the surface of the semiconductor substrate and neither parallel nor perpendicular to the first and second directions, and including a first silicon resistor and a second silicon resistor; wherein the first silicon resistor of the first piezoresistive sensor comprises a sensing piezoresistive element having respective sensing axes parallel to the first sensing axis, and a compensating piezoresistive element having a sensing axis, wherein a change in the resistance of the compensating piezoresistive element cancels out a change in the resistance of the sensing piezoresistive element due to a transverse stress with respect to the first sensing axis; and the semiconductor substrate includes a monolithic silicon substrate having a crystal orientation in a direction parallel to one of the first or second directions.

2. The IC according to claim 1, further comprising a sensing circuit having a first input coupled to the first terminal of the first silicon resistor of each of the first, second, and third piezoresistive sensors, a second input coupled to the first terminal of the second silicon resistor of each of the first, second, and third piezoresistive sensors, and an output.

3. The IC according to claim 2, wherein the first silicon resistors of the first and second piezoresistive sensors have resistances that change in response to deformation of the semiconductor substrate, and at least one of the second silicon resistors of the first and second piezoresistive sensors has a resistance that remains constant in response to deformation of the semiconductor substrate.

4. The IC according to claim 3, wherein the semiconductor substrate includes a monolithic silicon substrate having a crystal orientation in a direction parallel to one of the first or second directions.

5. The IC according to claim 4, wherein the semiconductor substrate includes a monolithic silicon substrate having a crystal orientation in a direction parallel to one of the first or second directions. The first and second silicon resistors of the first piezoresistive sensor have respective sensing axes parallel to the direction of the crystal orientation, and the sensing circuit is configured to provide a first sensing signal at its output, the first sensing signal representing a resistance difference between the first and second silicon resistors of the first piezoresistive sensor in response to a stress applied to the semiconductor substrate parallel to the direction of the crystal orientation. The first and second silicon resistors of the second piezoresistive sensor have respective sensing axes perpendicular to the direction of the crystal orientation, and the sensing circuit is further configured to provide a second sensing signal at its output, the second sensing signal representing a resistance difference between the first and second silicon resistors of the second piezoresistive sensor in response to a force applied to the semiconductor substrate perpendicular to the direction of the crystal orientation. An IC.

6. The IC according to claim 5, wherein the first and second silicon resistors of the third piezoresistive sensor have respective sensing axes oriented at +45 degrees and -45 degrees with respect to the direction of the crystal orientation of the semiconductor substrate, and the sensing circuit is further configured to provide respective sensing signals representing the shear force applied to the semiconductor substrate. An IC.

7. The IC according to claim 4, wherein the sensing piezoresistive element includes a plurality of compensating piezoresistive elements having respective sensing axes transverse to the first sensing axis, and a change in the resistance of the plurality of compensating piezoresistive elements is configured to cancel a change in the resistance of the sensing piezoresistive element due to a stress transverse to the first sensing axis. An IC including the plurality of compensating piezoresistive elements.

8. The IC according to claim 3, wherein the sensing circuit is configured to provide respective sensing signals, the sensing signals representing changes in the resistances of the respective first, second, and third piezoresistive sensors in response to deformation of the semiconductor substrate. The IC further includes a temperature sensor on or within the semiconductor substrate, the temperature sensor being configured to provide a temperature signal representing the temperature of the substrate. The IC is configured to compensate the sensing signal with respect to temperature in response to the temperature signal. An IC.

9. The IC according to claim 1, The semiconductor substrate includes a contact surface and an opposing surface spaced from the contact surface, and the contact surface is adapted to mechanically couple the IC to a mechanical structure by a coupling layer attached to the contact surface, an IC.

10. The IC according to claim 9 implemented in a sensing system, wherein the sensing system is a communication device attached to the opposing surface, the communication device being configured to communicate sensor data between the IC and an external reading device, and a controller attached to the opposing surface and coupled to the communication device, an IC including.

11. The sensing system according to claim 10, wherein the communication device communicates via a wired connection or a wireless connection, a sensing system.

12. The sensing system according to claim 10 implemented as a system-on-chip (SoC), wherein the SoC includes a packaging material encapsulating the IC and at least one of the communication device and the controller, a sensing system.

13. The sensing system according to claim 12, wherein the IC is a first IC, the SoC is a second IC as part of a multi-chip module also encapsulated within the packaging material, the second IC including a controller including at least one of a state machine, a microcontroller, and a microprocessor, the sensing system further including the second IC.

14. A system, an integrated circuit (IC), a semiconductor substrate having a certain crystal orientation, a first piezoresistive sensor on or within the semiconductor substrate, the first piezoresistive sensor having a first sensing axis extending in a first direction parallel to the surface of the semiconductor substrate, the first piezoresistive sensor including a first silicon resistor and a second silicon resistor, and a second piezoresistive sensor on or within the semiconductor substrate, the second piezoresistive sensor having a second sensing axis extending in a second direction parallel to the surface of the semiconductor substrate and different from the first direction, the second piezoresistive sensor including a first silicon resistor and a second silicon resistor, A third piezoresistive sensor on or within the semiconductor substrate, having a third sensing axis extending in a third direction parallel to the surface of the semiconductor substrate and neither parallel nor perpendicular to the first and second directions, and including a first silicon resistor and a second silicon resistor, the third piezoresistive sensor; Including the IC; A communication device coupled to the IC, configured to wirelessly communicate data representing deformation of the semiconductor substrate in response to a change in the resistance, the communication device; A controller coupled to the IC and the communication device, configured to control communication with the communication device, the controller; Including; The first silicon resistor of the first piezoresistive sensor; Sensing piezoresistive element having respective sensing axes parallel to the first sensing axis; A compensating piezoresistive element having a sensing axis, wherein a change in the resistance of the compensating piezoresistive element cancels a change in the resistance of the sensing piezoresistive element caused by a transverse stress with respect to the first sensing axis, the compensating piezoresistive element; A system including.

15. The system according to claim 14, Wherein the sensing circuit is coupled to the first, second and third piezoresistive sensors and configured to provide a sensing signal representing a change in the resistance of each of the first, second and third piezoresistive sensors in response to deformation of the semiconductor substrate, the system.

16. The system according to claim 15, Wherein each first silicon resistor has a resistance that changes in response to deformation of the semiconductor substrate, and each second silicon resistor has a resistance that remains constant in response to deformation of the semiconductor substrate, the system.

17. The system according to claim 16, Wherein the first and second silicon resistors of the first piezoresistive sensor have respective sensing axes parallel to the crystal orientation, the sensing circuit is configured to provide a first sensing signal at its first output, and the first sensing signal represents a difference in resistance between the first and second silicon resistors of the first piezoresistive sensor in response to a normal stress applied parallel to the crystal orientation to the semiconductor substrate, The first and second silicon resistors of the second piezoresistive sensor have respective sensing axes perpendicular to the crystal orientation, and the sensing circuit is further configured to provide a second sensing signal at its second output, the second sensing signal being a difference in resistance between the first and second silicon resistors of the second piezoresistive sensor in response to a normal stress applied perpendicularly to the crystal orientation to the semiconductor substrate, system.

18. The system according to claim 17, wherein the first and second silicon resistors of the third piezoresistive sensor have respective sensing axes oriented at +45 degrees and -45 degrees with respect to the direction of the crystal orientation of the semiconductor substrate, and the sensing circuit is further configured to provide respective sensing signals representing a shear force applied to the semiconductor substrate, system.

19. The system according to claim 15, wherein the IC further includes a temperature sensor on or within the surface of the semiconductor substrate, the temperature sensor being configured to provide a temperature signal representing the temperature of the semiconductor substrate, and the controller is further configured to compensate the sensing signal in response to the temperature signal, system.

20. The system according to claim 14 implemented as a system on chip (SoC), wherein the SoC includes a packaging material encapsulating the IC and at least one of the communication device and the controller, system.

21. The system according to claim 20, wherein the IC is a first IC, and the SoC further includes a second IC as part of a multi-chip module also encapsulated within the packaging material, system.

22. An integrated circuit (IC), which is a strain sensing sensor on or within a semiconductor substrate having a certain crystal orientation, which is a first piezoresistive sensor having a first sensing axis extending in a first direction parallel to the surface of the semiconductor substrate and parallel to the crystal orientation of the semiconductor substrate, the first piezoresistive sensor including a first silicon resistor and a second silicon resistor, the first silicon resistor having sensing piezoresistive elements having respective sensing axes parallel to the first sensing axis, A compensation piezoresistor element having a sensing axis, wherein a change in the resistance of the compensation piezoresistor element cancels out a change in the resistance of the sensing piezoresistor element due to a transverse stress with respect to the first sensing axis, the compensation piezoresistor element; The first piezoresistive sensor, including; A second piezoresistive sensor having a second sensing axis that is transverse to the crystal orientation of the semiconductor substrate and extends in a second direction parallel to the surface of the semiconductor substrate, including a first silicon resistor and a second silicon resistor, wherein the second direction is perpendicular to the first direction, the second piezoresistive sensor; A third piezoresistive sensor having a third sensing axis that is parallel to the surface of the semiconductor substrate and extends in a third direction that is neither parallel nor perpendicular to the first and second directions, including a first silicon resistor and a second silicon resistor, the third piezoresistive sensor; The strain sensing sensor, including; A sensing circuit coupled to each of the first, second, and third silicon resistor sensors, configured to provide respective sensing signals, the sensing signals representing changes in the resistance of the respective first, second, and third piezoresistive sensors in response to deformation of the semiconductor substrate, the sensing circuit; An IC, including.

23. The IC according to claim 22, wherein Each first silicon resistor has a resistance that changes in response to deformation of the semiconductor substrate, and each second silicon resistor has a resistance that remains constant in response to deformation of the semiconductor substrate, the IC.

24. The IC according to claim 23, wherein The compensation piezoresistor element is a plurality of compensation piezoresistor elements each having a sensing axis transverse to the first direction, and changes in the resistance of the plurality of compensation piezoresistor elements are configured to cancel out changes in the resistance of the sensing piezoresistor element due to a transverse stress with respect to the first direction, the IC including the plurality of compensation piezoresistor elements.

25. The IC according to claim 23, wherein The first and second silicon resistors of the third piezoresistive sensor have respective sensing axes oriented at +45 degrees and -45 degrees with respect to the direction of the crystal orientation of the semiconductor substrate, The sensing circuit is further configured to provide respective sensing signals representing a shear force applied to the semiconductor substrate, the IC.

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