Review: Semiconductor Piezoresistance for Microsystems

Stanford University, Mechanical Engineering, Stanford, CA 94305 USA.
Proceedings of the IEEE (Impact Factor: 4.93). 03/2009; 97(3):513-552. DOI: 10.1109/JPROC.2009.2013612
Source: PubMed


Piezoresistive sensors are among the earliest micromachined silicon devices. The need for smaller, less expensive, higher performance sensors helped drive early micromachining technology, a precursor to microsystems or microelectromechanical systems (MEMS). The effect of stress on doped silicon and germanium has been known since the work of Smith at Bell Laboratories in 1954. Since then, researchers have extensively reported on microscale, piezoresistive strain gauges, pressure sensors, accelerometers, and cantilever force/displacement sensors, including many commercially successful devices. In this paper, we review the history of piezoresistance, its physics and related fabrication techniques. We also discuss electrical noise in piezoresistors, device examples and design considerations, and alternative materials. This paper provides a comprehensive overview of integrated piezoresistor technology with an introduction to the physics of piezoresistivity, process and material selection and design guidance useful to researchers and device engineers.

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    • "Clearly, the corner frequency, where the power density of the thermal and flicker noises are equal, shifts toward higher frequencies by increasing the sensor bias. Above the bias voltage of 6V, the PSD mostly follows 1/ f α trend with 1.5 < α < 1.7, which can indicate the introduction of other noise mechanisms in addition to the conductance fluctuation of the material lattice [17]. "
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    ABSTRACT: We present a comprehensive study of the design, modeling, and characterization of an on-chip piezoresistive displacement sensor. The design is based on the bulk piezoresistivity of tilted clamped-guided beams without the need for additional steps to generate doped regions. The sensor is implemented in a one-degree-of-freedom microelectromechanical system (MEMS) nanopositioner, where the beams also function as the suspension system. A standard MEMS fabrication process is used to realize the device on single-crystalline silicon as the structural material. The beams are oppositely tilted to develop tensile and compressive axial forces during stage movement, creating a differential sensing feature. An analytical approach is proposed for modeling and design of the tilted clamped-guided beams. The linearity of the sensor in the differential configuration is investigated analytically. The static, dynamic, and noise characteristics of the sensor are presented, followed by a model-based investigation of the measured dynamic feedthrough. [2015-0030]
    Journal of Microelectromechanical Systems 10/2015; 24(5):1-1. DOI:10.1109/JMEMS.2015.2426180 · 1.75 Impact Factor
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    • "When a uniaxial stress is applied, the stress is connected to the strain via Hooke's law: σ = Eε, where E is the Young's modulus of SiC. Thus, the relationship between the gauge factor and the piezoresistive coefficient is G F = Eπ [1]. "
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    ABSTRACT: Silicon carbide (SiC) is one of the most promising materials for applications in harsh environments thanks to its excellent electrical, mechanical, and chemical properties. The piezoresistive effect of SiC has recently attracted a great deal of interest for sensing devices in hostile conditions. This paper reviews the piezoresistive effect of SiC for mechanical sensors used at elevated temperatures. We present experimental results of the gauge factors obtained for various poly-types of SiC films and SiC nanowires, the related theoretical analysis, and an overview on the development of SiC piezoresistive transducers. The review also discusses the current issues and the potential applications of the piezoresistive effect in SiC.
    Journal of Microelectromechanical Systems 09/2015; 24. DOI:10.1109/JMEMS.2015.2470132 · 1.75 Impact Factor
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    • "Strain sensing applications such as microcantilever technology, force sensors, and pressure sensors have widely benefited from piezoelectric [1] and piezoresistive [2] materials. Inspired by similar effects, recently extensive attempts on stretchable polymer thin films based on nanoscale structures [3] [4] [5] achieved higher strain sensitivity only for large deformations, aiming for highstrain sensing devices [6]. "
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    ABSTRACT: Tunnel magnetoresistance (TMR) junctions with CoFeB/MgO/CoFeB layers are promising for strain sensing applications due to their high TMR effect and magnetostrictive sense layer (CoFeB). TMR junctions available even in submicron dimensions can serve as strain sensors for microelectromechanical systems devices. Upon stress application, the magnetization configuration of such junctions changes due to the inverse magnetostriction effect resulting in strain-sensitive tunnel resistance. Here, strain sensitivity of round-shaped junctions with diameters of 11.3 μm, 19.2 μm, 30.5 μm, and 41.8 μm were investigated on macroscopic cantilevers using a four-point bending apparatus. It mainly focuses on changes in hard-axis TMR loops caused by the stress-induced anisotropy. A macrospin model is proposed, supported by micromagnetic simulations, which describes the complete rotation of the sense layer magnetization within TMR loops of junctions, exposed to high stress. Below 0.2‰ tensile strain, a representative junction with 30.5 μm diameter exhibits a very large gauge factor of 2150. For such high gauge factor a bias field is applied in an angle equal to toward the pinned magnetization of the reference layer. The strain sensitivity strongly depends on the bias field. Applying stress along against along the induced magnetocrystalline anisotropy, both compressive and tensile strain can be identified by a unique sensor. More importantly, a configuration with a gauge factor of 400 at zero bias field is developed which results in a straightforward and compact measuring setup.
    Journal of Magnetism and Magnetic Materials 02/2015; 384. DOI:10.1016/j.jmmm.2015.01.083 · 1.97 Impact Factor
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