Tactile sensor systems based on complementary metal-oxide-semiconductor (CMOS) technologies have found a wide variety of applications covering various types of man-machine interfaces as well as industrial applications. These sensor systems are realized using commercially available CMOS processes combined with appropriate assembly technologies for advanced system packages, and dedicated micromachining processes to realize membranes or beam structures to improve the sensor sensitivity. Piezoresistive CMOS-based tactile sensor systems make use of implanted resistors and field-effect transistors (FETs) exploiting the piezoresistive effect in silicon. The applied CMOS chips extract the mechanical stress distribution in the chip surface which is characteristic for the corresponding mechanical loading of the CMOS chip or its package. This paper describes a three-dimensional force sensor used in metrology to extract the 3D geometry of precision machined parts, and the Smart Tooth, an innovative tool for orthodontic research and education.

We present a torsional bridge setup for the electro-mechanical characterization of devices integrated in the surface of silicon beams under mechanical in-plane shear stress. It is based on the application of a torsional moment to the longitudinal axis of the silicon beams, which results in a homogeneous in-plane shear stress in the beam surface. The safely applicable shear stresses span the range of ±50 MPa. Thanks to a specially designed clamping mechanism, the unintended normal stress typically stays below 2.5% of the applied shear stress. An analytical model is presented to compute the induced shear stress. Numerical computations verify the analytical results and show that the homogeneity of the shear stress is very high on the beam surface in the region of interest. Measurements with piezoresistive microsensors fabricated using a complementary metal–oxide–semiconductor process show an excellent agreement with both the computational results and comparative measurements performed on a four-point bending bridge. The electrical connection to the silicon beam is performed with standard bond wires. This ensures that minimal forces are applied to the beam by the electrical interconnection to the external instrumentation and that devices with arbitrary bond pad layout can be inserted into the setup.

Sensor systems based on piezoresistors have found a wide variety of applications whenever mechanical stress due to external mechanical input is to be determined. Such sensor elements are fabricated using commercial CMOS processes enabling the realization of highly integrated systems with electronics for signal amplification and multiplexing. They combine stress-sensing elements such as Wheatstone bridges, 4- and 8-terminal well-based devices, or 4-contact piezoresistive field effect transistors, i.e. piezo-FETs. In addition, innovative devices generating out-of-plane current components are applied to determine out-of-plane stress components. The paper discusses the sensing elements, the system architecture and the post-CMOS fabrication processes required to realize the CMOS-integrated stress sensor systems. Smart orthodontic brackets and a stress sensing neural probe are discussed in more detail.

This paper reports on the development and characterization of a CMOS-integrated three-dimensional force sensor for coordinate measurement applications. In contrast to previously presented tactile sensors using the same principle of operation, this sensor features 32 PMOS piezoresistive field effect transistors as stress sensing elements. We performed calibration measurements in the x, y, and z directions and found the accuracy of this system comprising the CMOS sensor chip and a tactile metal pin to be better than ±50 nm. The ratio of stiffness against vertical and horizontal deflection of the probing system was found to be Sz/Sxy ≈ 4.8.

This paper reports on the characterization of the stress-dependent magnetic sensitivity of CMOS-based Hall devices, i.e. cross-shaped four-terminal n-wells and field effect transitors (FET) with four source-drain contacts, using a novel experimental setup. The setup comprises a four-point bending bridge used to apply well-defined mechanical in-plane stress to silicon strips, combined with permanent magnets for the application of controlled magnetic fields up to +/- 240 mT. Measurements of both n-well-based Hall plates and FET-based Hall plates are performed. The piezo-Hall coefficient P-12 extracted from stress measurements under vertical magnetic fields from the n-well sensors is in excellent agreement with previously reported values while the FET-based devices exhibit a clearly reduced coefficient. (C) 2010 Published by Elsevier Ltd.

This paper reports a novel generation of CMOS stress mapping chips comprising 32 square field effect transistors (FET) with four source/drain contacts (piezo-FETs) exploiting the shear piezoresistive effect in n-type (NMOS) or p-type (PMOS) inversion layers. The sensor chips with a total die area of 2.5 times 2 mm 2 are integrated with analog circuitry and digital logic. When exposed to homogenous shear or normal stress, all 32 integrated stress sensors show a linear response in excellent agreement with theoretical predictions and exhibit identical stress sensitivities. Piezo-FETs fabricated as separate devices are characterized with respect to stress sensitivity, intrinsic offset, and noise behavior. Stress sensitivities are enhanced by incorporating a central hole into the piezo-FETs. Sensitivities of -448 muV/(V MPa) and 477 muV/(V MPa) were measured for NMOS and PMOS devices, respectively.

This paper reports on the development and characterization of novel in-plane CMOS-based stress sensors featuring equal sensitivities towards the two mechanical shear stress components sigma xy = (sigma x'x' - sigma y'y' ) / 2 and sigma x'y' . The sensor structures are based on symmetric n-well resistors with eight contacts. A geometric parameter variation is performed using FEM simulations to adjust the stress sensitivities of different sensor layouts. For characterization, in addition to a four-point bending bridge used to exert normal stresses (sigma x'x' - sigma y'y' ), a novel torsional bridge setup was developed to apply well-defined shear stress sigma x'y' to the surface of silicon beams diced parallel to the <110> crystal direction of silicon and containing the stress sensor elements. The measured sensitivities are consistent with simulated values.