New enhancing sensitivity tool for Hall effect devices Ch. Roumenin * , D. Nikolov, A. Ivanov Institute of Control and System Research, Bulgarian Academy of Sciences, PO Box 79, Bl. 2, G. BonchevStr., 1113 So®a, Bulgaria Received 11 June 2001; received in revised form 18 October 2001; accepted 13 November 2001 Abstract For the ®rst time is suggested a paradoxical, but quite effective, principle for increase of the magnetosensitivity of the silicon parallel- ®eld Hall microsensorsÐby a minority carrier injection. A maximal approach of the majority carriers ¯ows to the chip surface with the contacts and its lateral shrink are achieved with an S-type negative resistance and current ®lament in the structure. As a result, the geometrical correction factor G increases and simultaneously the effective thickness t of the Hall microdevice decreases. The advantages of the new enhancing sensitivity tool are: the necessity of additional expensive technological steps, to correct the current trajectory, drops out; the Hall coef®cient remains unchanged; the majority carrier mobility keep its bulk value for silicon and the dissipated power in the substrate is reduced. This new operating principle is applied in two silicon parallel-®eld Hall devices, reaching a dramatic increase of the magnetosensitivityÐonly a 10 mA injection leads to an increase of the Hall voltage with more than 55%. The same result however, but without p  ±n junctions would be registered with a three order of magnitude larger change of the supply current. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Magnetic microsensors; Parallel-®eld Hall devices; Filament magnetosensitivity effect 1. Introduction One of the main goals in all types of sensors (including the Hall devices) is the increasing of their transducer ef®ciency in such conditions under which it is close or coincides with its respective physical limit. For example, one of the most promising aspectsÐthe parallel-®eld Hall versionsÐ undergo a constant evolution. These devices are based on the proposed for the ®rst time in 1983 principle of Hall voltage occurrence in semiconductor structures, containing at least one ¯at plane and an external magnetic ®eld B applied parallel to it. The supply and the Hall voltage contacts are located on this surface [1,2]. The curvilinear shape of the carrier trajectory substantially affects their transducer ef®ciency S by the geometrical correction factor G and the actual thickness t  of the n-type device in the direction of the ®eld B, S  V H  G=t  , [2,3]. Up to date few methods have been applied by which the trajectory in this class of sensors can be technologically corrected: inserting an n  -buried layer under the active zone; addi- tional surface doping; combining an n  -buried layer and p-trench groove by ion etching; formation of a deep rec- tangular p-guard ring surrounding the contacts area and reducing the spreading surface currents, etc. [4±6]. These approaches, however, in the general case are not suf®ciently effective and universal mainly because of the increase of the concentration n of the majority carriers and decrease of the mobility. As a result the Hall coef®cient R H  1=n decreases and hence the output voltage V H (B) too. In this paper, a new enhancing sensitivity tool for parallel- ®eld Hall effect devices is described. It consists of an elec- trical control of the two main parametersÐincrease of the G-factor and a simultaneous decrease of the thickness t  , both determining the magnetosensitivity. This ®gure of merit is dramatically improved in an unexpected mannerÐby a minority carrier injection. 2. Magnetosensitivity limitations in parallel-field Hall devices As well known, under extrinsic and homogeneous con- ditions the two main geometrical parameters, the factor G and the effective thickness t  in ®eld B direction in¯uence the value of the output Hall signal V H (B) as well as the supply-current-related sensitivity S RI by the expressions V H  GR H I C1;2 B t   G t  ; S RI  R H G t   G t  (1) where R H denotes the Hall coef®cient, I C1;2 is the bias current. The other notations are as usual [2,3]. Sensors and Actuators A 97±98 (2002) 296±301 * Corresponding author. Tel./fax: 359-2-737822. E-mail address: roumenin@iusi.bas.bg (Ch. Roumenin). 0924-4247/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0924-4247(01)00865-2