Advanced piezoresistive and magnetoresistive sensors [electronic resource]

Smart sensors are now being used almost everywhere, with increasing demands and growing markets across various industrial applications, such as consumer electronics, automotive, healthcare, and power. Among all sensing technologies, resistive sensors, which can convert various forms of environmental energy into resistance changes, are popular and widely employed as critical components and basic building blocks for sensing platforms. Furthermore, data collections with less expensive and more accurate miniature sensors are required, which bring new challenges to engineering researchers in sensor design, fabrication, and integration. In this work, advanced piezoresistive and magnetoresistive sensors for various industrial applications will be discussed. First, a stand-alone stretchable absolute pressure sensor network has been developed for smart vehicle applications. The network with microelectromechanical systems (MEMS) piezoresistive sensing elements can be mounted on various curved surfaces to cover an area that is 100 times larger than its original size. Also, the pressure sensing network can provide good sensitivity and be fabricated in a cost-effective manner on silicon wafers. In addition, low-noise readout electronics was implemented in this stand-alone absolute pressure sensor network for achieving signal conditioning, power management, and wireless communication. Therefore, the sensor network demonstrates the first step towards the development of an absolute pressure distribution monitoring system, and shows great potential to be employed in a variety of smart systems. Second, a multilayer anisotropic magnetoresistive (AMR) sensor has been described for high accuracy angle detection. Intrinsic angular errors of AMR angle sensors can be attributed to two dominant sources: the second harmonic error due to induced anisotropy, and the eighth harmonic error from shape anisotropy. The fabricated quadruple layer AMR angle sensor with correction algorithm reduces mean magnitude of angular errors by a factor of 5 relative to the traditional single-layer device. Moreover, the quadruple layer AMR angle sensor can be operated at low magnetic fields under 100 Oe, enabling the use of cheaper hard magnets for magnetic field sensing. Thus, the proposed quadruple layer AMR angle sensor is promising for many industry applications. Finally, the third part of this dissertation will focus on lowering magnetic 1/f noise in AMR magnetic field sensors, which normally operate in the unsaturated region. IrMn exchange-biased AMR sensors have been optimized for increased magnetoresistive ratio and reduced noise. Sensor noise performance can be further improved by the addition of a thin MgO layer between the NiFe and the Ta capping layer. The decrease in magnetic 1/f noise can be attributed to magnetization stabilization by IrMn and a reduction in pinning sites by MgO. Therefore, the good performance of IrMn exchange-biased AMR sensors render them promising for a wide range of applications.

Keywords: Electrical Engineering.
Advisor: Wang Shan
Chang Fu-Kuo advisor. Thesis advisor
Howe Roger Thomas advisor. Thesis advisor