A piezoresistive CMOS-compatible sensor for measuring the temperature-compensated out-of-plane shear stress components sigma(xz), and sigma(yz) is analyzed, implemented, and applied. The device exploits the shear piezoresistive effect due to vertical (out-of-plane) shear stress components. Possible sensor geometries are discussed and sensitivity considerations based on an affine transformation are presented. A bi-directional, 53 mu m x 53 mu m-large sensor design measuring two output voltages linearly proportional to the vertical shear stress components sigma(xz) and sigma(yz) is introduced. The experimental characterization of 17 such structures revealed an offset of the measurement voltage of -1.3 +/- 0.6 mV and a linear sensitivity of -320 +/- 85 mu V/MPa. A variation of the supply voltage from 0 V to 5 V modulates the sensor resistance and voltage-related sensitivity by +6% and -12%, respectively. The geometry dependence of the sensitivity is evaluated using a finite element analysis. Design guidelines are extracted from these simulations. A demonstration of the sensor performance in an application concludes this paper. (C) 2012 Elsevier B.V. All rights reserved.

This paper reports on the mechanical and piezoresistance characterization of hydrogenated amorphous and nanocrystalline silicon thin films deposited by hot-wire chemical vapor deposition (HWCVD) and radio-frequency plasma-enhanced chemical vapor deposition (PECVD) using substrate temperatures between 100 and 250 °C. The microtensile technique is used to determine film properties such as Young’s modulus, fracture strength and Weibull parameters, and linear and quadratic piezoresistance coefficients obtained at large applied stresses. The 95%-confidence interval for the elastic constant of the films characterized, 85.9 ± 0.3 GPa, does not depend significantly on the deposition method or on film structure. In contrast, mean fracture strength values range between 256 ± 8 MPa and 600 ± 32 MPa: nanocrystalline layers are slightly stronger than their amorphous counterparts and a pronounced increase in strength is observed for films deposited using HWCVD when compared to those grown by PECVD. Extracted Weibull moduli are below 10. In terms of piezoresistance, n-doped radio-frequency nanocrystalline silicon films deposited at 250 °C present longitudinal piezoresistive coefficients as large as −(2.57 ± 0.03) × 10−10 Pa−1 with marginally nonlinear response. Such values approach those of crystalline silicon and of polysilicon layers deposited at much higher temperatures.

A piezoresistive sensor for measuring the temperature compensated sum (σxx+σyy)/2−βσzz of the three mechanical normal stress components, where σxx+σyy, σzz, and β denote the in-plane normal stress sum, the out-of-plane normal stress, and a numerical factor close to 1 is presented. The device is based on CMOS-compatible diffusions and exploits the piezoresistive effect acting on vertical current components. The sensor signal and resulting possibilities to extract mechanical stress components are analyzed. Experimental results illustrate the influence of design parameters and operating conditions on the sensor performance and are compared to a simple analytical sensor model. A second-order cross-sensitivity to in-plane shear stresses is discussed and determined experimentally. The temperature compensation is demonstrated by a force measurement with a deviation between the numerically expected and the experimentally extracted value smaller than 15% over the temperature range from 10°C to 60°C.

This paper presents a CMOS stress sensor chip including arrays of piezoresistive sensor elements with high spatial resolution sensitive to the in-plane stress components sigma(xx)-sigma(yy) and sigma(xy), to the out-of-plane stress sigma(xz) and sigma(yz), and to the normal stress sum sigma(Sigma) =- (sigma(xx) + sigma(yy))/2 - sigma(zz). For the first time, an application of novel vertical stress sensors is presented, measuring the mechanical stress distributions below electroless nickel (eNi) bumps subject to lateral shear forces and vertical compression. All measured stress values are linearly proportional to the applied forces. The vertical shear stress sensors resolve residual vertical shear stresses of up to 51 MPa in the shear experiments. An adjustable numerical model is established assuming two different Young's moduli of silicon nitride (SiN) emulating the adhesion between the SiN and eNi. Qualitative agreement of the in-plane stress distributions between experiment and numerical simulation is found in the shear and compression experiments, while good correlation for sigma(Sigma) is found only for temperature uncompensated stress values in the compression test. The modeling of the absolute values shows differences to the experimental data of about +/- 30%.

This paper presents high-density arrays of 7 x 7 nand p-type piezoresistive field effect transistor (piezo-FET)-based stress sensors realized with a pitch of 23 mu m using a commercial complementary metal-oxide semiconductor (CMOS) technology. The sensor elements make it possible to extract the distribution of the in-plane normal stress difference sigma(xx) - sigma(yy) and the in-plane shear stress sigma(xy) under electroless nickel (eNi) bumps. For the first time, pre-deposition stress caused by openings in the passivation, stress induced by the eNi bump deposition, and stress redistribution during anneals between 50 degrees C and 260 degrees C are presented. Typical values of sigma(xx) - sigma(yy) of +/- 25 MPa are introduced by bump deposition. These values are further increased by up to 160% during anneals up to 260 degrees C. The in situ monitoring of the mechanical stress redistribution during annealing and thermal cycling is studied. At the deposition temperature, the system is found to be almost stress free. The stress due to bump deposition is numerically modeled. The unknown adhesion strength between nickel bump and silicon nitride (SiN) passivation is taken into account using an adjustable Young's modulus of SiN. For an optimized model, the correlation between measured and simulated spatial stress distributions is found to be high, while the magnitude of the stress values is underestimated in the model by about 35%.

This paper reports on the piezoresistive characterization of low-doped crystalline silicon using the wafer-scale microtensile technique. Multiple test structures composed of <;110>; and <;100>; specimens bridging the gap between movable and fixed micromachined frames are processed in a single wafer and sequentially measured. In addition to the extraction of elastic and fracture parameters, the method allows to obtain the piezoresistance behavior of silicon samples at large applied stresses. This is realized by defining longitudinal and transversal resistors on the specimens by ion implantation and monitoring the respective resistances until fracture occurs. For sufficiently large loads, resistivity variations clearly deviate from the expected linear dependence on stress and become non-monotonic. These findings are particularly relevant for the application of crystalline silicon in piezoresistive sensing devices subjected to large stress levels.

This paper reports on a novel CMOS-based silicon microprobe for high-density intracortical stress mapping. In contrast to existing systems, square p-type field effect transistors (FET) with four source/drain contacts (piezo-FETs) are integrated on the slender, needle-like probe shaft. In total, 345 stress sensors are arranged in five columns (x/y-pitch of 51.4/26.6 mu m) along the 180-mu m-wide shaft. Measuring in-plane normal stress in silicon neural probes is envisioned to avoid probe fracture during insertion and to evaluate the probe deflection caused by brain motion after insertion. The combination with switchable electrodes will enable the simultaneous neural recording of brain activity. The paper presents the probe concept, the post-CMOS fabrication process, the piezo-FET characterization, and measurements demonstrating stress mapping in a brain model.

This paper discusses the measurement opportunities arising from a novel piezoresistance sensor featuring vertical currents. Temperature-compensated measurements of a sum of the three normal stress components including the vertical normal stress, are presented. In specific applications with sensors located at free surfaces where the vertical normal stress component vanishes, a combination of this temperature-compensated measurement and a pseudo-Hall measurement yields the individual in-plane normal stresses. Furthermore, the temperature-uncompensated extraction of the vertical normal stress component is discussed with respect to the new measurement possibilities provided by the presented sensor. A sensitivity analysis illustrates the influence of individual uncertainty sources to the overall uncertainty of the measurement. Based on these results possible improvements in stress detection are suggested.

This paper reports on the development and characterization of a novel stress and temperature mapping chip fabricated in a standard 0.6 ¿m CMOS process. The sensing array consists of 10 × 10 square unit cells enabling the simultaneous measurement of the absolute temperature as well as five independent mechanical stress components in a temperature compensated manner. These components are (i) the difference of in-plane normal stresses ¿xx - ¿yy , (ii) the in-plane shear stress sxy , (iii, iv) the out-of-plane shear stress components ¿xz and ¿yz and (v) the linear combination of the three normal stress components ¿¿ = (¿xx + ¿yy)/2 - ß ¿zz. As application examples, stress distributions generated by applying a local force and an inhomogeneous temperature distribution across the chip were mapped.

The test of whether a proposed mandatory vaccination program is constitutional needs updating. Jacobson v. Massachusetts, decided by the U.S. Supreme Court over a century ago, laid out the proper reasoning and concerns to be addressed when determining the legality of mandatory vaccinations, but its analysis is tailored to the extreme case of the smallpox epidemic. As more vaccinations are created to address decreasingly pressing needs, it becomes clear that because of the liberty interests involved when requiring their use, vaccinations should not be made mandatory simply because they can be created. Scientific possibility does not create individual necessity. A new test must seek to address the evolving subtleties related to the use of vaccinations while still maintaining the fundamental reasoning of Jacobson. This Note introduces the Modified Hand Formula, a new test that balances the key competing concerns inherent in any discussion of the constitutionality of mandatory vaccinations. The Modified Hand Formula asks whether the “Burdens” associated with implementing mandatory vaccination—both social economic burdens and the personal burden of sacrificing constitutionally protected liberty interests— exceed the reduction in “Probable Loss,” the lessening of human costs, achieved by such a program. The importance of developing a new test is underscored by a recent rise in discussion regarding mandatory vaccination for human papillomavirus (“HPV”). In June 2006, the Food and Drug Administration (“FDA”) approved and licensed Gardasil, manufactured by Merck, the first vaccine developed to prevent the transmission of HPV. With FDA approval for women finalized in

This paper reports the development and characterization of a highly integrated polyvalent CMOS stress sensor detecting five linearly independent, temperature compensated components of the six-dimensional stress space. The sensor has a footprint of only 29x29 mu m(2). It combines different piezoresistance sensors to detect the three shear stresses, the in-plane normal stress difference, and a sum of the three normal stresses. The sensitivities of five sensing modes are characterized by applying in-plane normal and shear stresses, out-of-plane shear stresses, and temperature changes. The sensor performance is demonstrated by monitoring the hardening of an epoxy resin.

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 presents CMOS-based, high density arrays of 7 × 7 n- and p-type piezoresistive field effect transistor (piezo-FET) based stress sensors with a pitch of 23 μm for extracting the distribution of the in-plane normal stress difference σxx - σyy and the in-plane shear stress σxy under electroless Ni bumps. For the first time, pre-deposition stress caused by openings in the passivation, stress induced by the electroless Ni bump deposition, and stress redistributions during annealing processes between 50°C and 200°C are presented. Typical values of σxx - σyy = ±25 MPa are introduced by bump deposition. These values are further increased by up to 60% during annealing steps of up to 200°C. The in-situ monitoring of the mechanical stress redistribution during an anneal at 115°C shows a relaxation of the material compound by σxx - σyy = ±2.5 MPa over 180 min. The change of the stress components is found to be linear with temperature during thermal cycling resulting in an almost stress-free state at the deposition temperature.

We report on the piezoresistive characterization of various silicon materials, including low-doped (n = 10(16) cm(-3)) crystalline (c-Si), polycrystalline (poly-Si), and nanocrystalline (nc-Si) specimens. The employed wafer-scale microtensile technique enables the acquisition of linear and nonlinear piezoresistance coefficients. In contrast to previous studies where nonlinear coefficients were obtained for strains up to only 0.2%, the data presented here are extracted up to the fracture strain of about 1%, leading to more reliable higher-order piezoresistive parameters. Longitudinal and transverse resistance measurements of the specimen regions under uniform stress are realized during sample mechanical loading. Relative resistivity changes Delta rho/rho of up to -12.6, -36, and -40% are found for longitudinal resistance measurements at specimen fracture stresses of 1.4, 1.4, and 2.1 G P a for poly-Si and c-Si aligned with < 100 > and < 110 > directions, respectively. Non-monotonic characteristics with maximal resistivity changes of -16 % and 11.5 % are found for transverse resistance measurements on c-Si along the < 100 > and < 110 >-directions, respectively. The nonlinear behaviour of c-Si is modeled by a fourth order polynomial, while a second order polynomial sufficiently fits the poly-Si data. Such findings are particularly relevant for the application of these materials in piezoresistive sensing devices subjected to relatively large stress levels.

This paper reports the development and characterization of a novel piezoresistive CMOS stress sensor enabling the measurement of the out-of-plane shear stress components δxz and δyz by exploiting the shear piezoresistive effect, i.e. the pseudo-Hall effect. The sensing structures are fabricated using a commercial CMOS process. They include a vertical current channel and two pseudo-Hall sensing contacts. In order to characterize the sensor elements, a setup comprising a silicon bridge with SU-8 posts was developed to induce well defined and homogeneous vertical shear stress in the chip surface. This vertical shear stress setup is analyzed using finite-element (FE) simulations. Measurements demonstrating the sensor concept show a linear sensor response with a sensitivity of 0.092 V/(A MPa).

This paper presents a novel piezoresistive sensor detecting a temperature compensated sum of the three mechanical normal stress components including the Out-of-plane stress iquest zz . The sensor is based on CMOS-compatible diffusions designed to exploit vertical currents. We show that the temperature compensated stress sum can be extracted via two different sensor designs and even with a single device exploiting the strong influence of the junction field effect in the sensor. For this purpose, an experimental setup that induces homogenous vertical normal stress sigma zz by applying a vertical force via a gold bump to the sensor is presented. For the characterization, the resulting mechanical stress at the sensor location was evaluated using finite element simulations. Sensitivities, depending on gold bump shape and bias current, were experimentally determined and vertical forces were successfully extracted between 10degC and 60degC, independent of temperature.

This paper presents a selection of microsensors and microsystems based on complementary metal oxide semiconductor technology for measuring mechanical stress and tries to identify some of the next challenges. As the stress acting on the sensors may originate from effects internal or external to the package, the sensors lend themselves for the measurement of (1) time-dependent thermomechanical forces acting on a packaged microchip and (2) external mechanical constraints, i.e., forces and moments. Recently developed applications include tactile sensors, smart brackets, and a solid-state-only joystick with four degrees of freedom, among others. The systems implemented in these applications rely on sensors for in-plane stresses. For packaging testing applications, in addition, sensors for out-of-plane stress components are beneficial. First designs of such new sensors and corresponding results are presented. The calibration of piezoresistive elements is performed on dedicated experimental setups, such as optimized four-point bending and torsional bridges for the application of well-controlled in-plane stresses, and setups in the first stage of their development for the exertion of vertical stress components.