E LSEVI ER Sensorsand Actuators A 56 (1996) 233-237 A novel structure for three-dimensional silicon magnetic transducers to improve the sensitivity symmetry Hsiao-Yi Lin a, Tan Fu Lei ", Jz-Jan Jeng b, Ci-Ling Pan b, Chun-Yen Chang" Department of Electronics Engineering and Institute of Electronics. National Chiao Tung University. Hsinchu. Taiwan h Institute of Electro-Optical Engineering. National Chiao Tung University. Hsinchu. Taiwan Received9 August 1995;revised 19 April 1996;accepted 4 June 1996 Abstract A three-dimensional silicon magnetic transducer with symmetric sensitivities in the x-, y- and z-directions and small cross sensitivity has been demonstrated. Devices are based on a design of a vertical Hall structure using the surrounding trench and symmetric design to suppress the cross sensitivity. The fabrication process is simple and can he used as a part of a standard integrated circuit process. The results show that almost equal sensitivities in all three components of magnetic field can he obtained by coating Ni/Co thin films on the backside of the substrates. The cross sensitivity is only i.3% of the sensitivity. Keywords: Magnetic transducers; Silicon; Symmetric sensitivity 1, Introduction Development of fully integrated magnetic-field transduc- ers which are able to measure simultaneously more than two components of the magnetic field B has attracted much atten- tion. Possible applications of such three-dimensional (3-D) magnetic transducers include magnetic vector measurements, measurement of the earth's magnetic field for navigational or geological purposes, proximity switches and contactless angular position encoders, etc. [ 1-3]. Recently, 3-D mag- netic-field transducers were designed employing various structural configurations [ 1-13]. However, these 3-D mag- netic-field transducers either utilize a more complex structure [ 1,3,6] or exhibit an unsymmetric sensitivity [ 1-6]. A!most all published papers focus on improvements in sensitivity, resolution and device structure, etc. In this work, our focus is on the improvement of the sensitivity symmetry and sim- plifying the structure. The device structure shown in this paper is simple and similar to the structure proposed by Par- anjape et al. [8], but with some modification to improve the symmetry of the sensitivity and reduce the cross sensitivity. 2. The 3-D vertical Hall magnetic-field transducer design The basic structure of the Hall device for detecting 3-D magnetic field is shown in Fig. 1. The contact Co is used as 0924-42471961515.00© 1996 ElsevierScienceS.A. All rightsreserved P!1S0924-4247(96)01323-4 me2 i' o E y x: H 2 H 2' nl M A' IJ"q w m B' i H! . cs EB H$ .! 8 m R n÷ [ ] Trench R [] H4 H4' i200 i,m Top view i~lC4 (a) (b) (e) Fig. I. (a) Plan view of the 3-D Hall device; (b) cross-sectional view of the device without NilCo coating; (c) cross-sectional view of the device with NilCo coating. the central current contact and C~, C2, C3, C4 are connected and serve as the outside current contacts. The four pairs of