1356 IEEE SENSORS JOURNAL, VOL. 12, NO. 5, MAY 2012 Design Study of a Bar-Type EMR Device Jian Sun, Student Member, IEEE, Chinthaka P. Gooneratne, Member, IEEE, and Jürgen Kosel, Member, IEEE Abstract—It is well known that extraordinary magnetoresis- tance (EMR) depends on the geometric parameters of the EMR device and the locations of the electrodes. In this paper, the perfor- mance of a bar-type EMR device is simulated with respect to the device geometry and electrode locations. The performance is eval- uated with regards to the output sensitivity of the device, rather than the often analyzed EMR ratio, since it is more relevant than the EMR ratio for potential applications ranging from read heads to smart biomedical sensors. The results obtained with the finite element method show the dependence of the output sensitivity on the device geometry the placements of the electric contacts as well as the strength of the applied magnetic field in different configurations and allow finding the optimum parameters. Within the studied range of to 1 T both IVVI and VIIV configurations show very similar behavior. For EMR sensors of high sensitivity, the results suggest that a simple two-contact device would provide the best performance replacing the conventional four-contact design. Index Terms—Extraordinary magnetoresistance, finite-element method, Hall effect, magnetic sensors. I. INTRODUCTION I N recent decades, magnetoresistance (MR) sensors have be- come increasingly important due to their high sensitivity, low power consumption, small size and low cost. They are crit- ical components in technologies such as high-density informa- tion storage [1]–[3] and certain kinds of bio-chips [4], [5]. The magnetoresistance of these sensors contains a physical contri- bution from the magnetic field dependence on the material pa- rameters and a geometric contribution from the dependence of the current path and output voltage on the geometry of the de- vice. To date, the majority of MR sensors work on the basis of physical contributions such as Giant Magnetoresistance (GMR) [6] and Tunnel Magnetoresistance (TMR) [7]. Recent research has shown that the geometric contributions can play an impor- tant or even dominant role in some magnetoresistive devices leading to the ballistic magnetoresistance (BMR) [8] and ex- traordinary magnetoresistance (EMR) [9]. However, it must be noted that several questions still remain over the validity of the BMR effect [10]. Nevertheless, the EMR effect has drawn much attention and has shown to be potentially viable for future magnetic recording applications [11]. Since the EMR effect has Manuscript received June 04, 2011; revised September 10, 2011; accepted September 29, 2011. Date of publication October 10, 2011; date of current ver- sion April 13, 2012. This is an expanded paper from the IEEE SENSORS 2010 Conference. The associate editor coordinating the review of this manuscript and approving it for publication was Dr. Patrick Ruther. The authors are with the Physical Sciences and Technology Division, 4700 King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia (e-mail: jian.sun@kaust.edu.sa; chinthaka.gooneratne@kaust.edu.sa; jurgen.kosel@kaust.edu.sa). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JSEN.2011.2171050 been demonstrated in nonmagnetic semiconductor-metal hybrid structures, thermal magnetic noise can be reduced more effi- ciently than in TMR and GMR devices [12]. In addition, the saturation field of an EMR device exceeds 1 T, resulting in a large working range in comparison to other magnetoresistance devices. EMR devices have been fabricated using high-mobility and narrow-gap semiconductors shunted by a highly conduc- tive metal bulk [13]. These properties of the semiconductor guarantee that the material shows a strong Hall effect along with a comparatively good conductivity. Experiments were initially performed on a composite van der Pauw disk of a semiconductor matrix with an embedded metallic circular in- homogeneity that was concentric with the semiconductor disk [9]. A similar EMR effect has been reported for a rectangular semiconductor bar with an externally shunted metal stack [14]. This geometry can be derived from the van der Pauw disk using the bilinear transformation. In an EMR device, the Lorentz force induced by a magnetic field causes a redistribution of the current density in the semiconductor and metal resulting in resistance changes. This effect is an extrinsic property that depends on the shape of the device and the placement of the electric contacts. Previous studies that have investigated the influence of contact configurations and the geometry of the metallic region on the performance of the EMR device, have evaluated the device based on the EMR effect [15]–[18]. How- ever, a more important parameter for sensing applications is the output sensitivity, which has not been considered so far. In this paper, EMR devices made of InSb/Au hybrid struc- tures in a bar geometry were modeled and simulations carried out by means of the Finite Element Method (FEM). The FEM has been utilized previously to study the EMR effect, and it has shown very good agreement with experimental results [19]. The purpose of this research is to develop a model to calculate quantities such as current density distribution and spatial poten- tial, which in turn are used to investigate geometric influences on the output sensitivity of a semiconductor/metal hybrid struc- ture. This allows finding the critical parameters, which need to be optimized for specific applications. II. THEORETICAL ASPECTS OF EMR EMR devices are commonly made from n-type semiconduc- tors, since the mobility of electrons is typically larger than that of holes yielding a much larger Hall effect [20]. Therefore, only the dominant carrier-electron is taken into consideration in the EMR simulation. Further, since EMR devices are made of thin film structures, the thickness in the axial direction is neglected and only a 2-D model described in the - plane is built. The vector of the current density is governed by Ohm’s law (1) 1530-437X/$26.00 © 2011 IEEE