2D magnetodiode sensors based on SOS technology

A novel integrated device capable of measuring simultaneouslythe two in-plane somponentr 8. and B, of the magnetic-field vector is presented.The sensoris basedon the magnetodiodeprinciple and is labricatal by a silicon-on .sapphire(SOS) technology.This transducer consistsof tw one-dimensional differential (n’-n-p’-n-n’) micromagnetadicdespositioned at an angle of 90” with a commas central p’-n junction. Linear and odd output signals from the two channels in the -0.1 T
1. IntrwJuction

the non-linear output characteristics I(B)

or V(E).

and the

strong temperature dependence of the output signal. Semiconductor microsensors for magnetic field occupy an

This paper for the first time presents solutions to these two

important place amidst the great variety of transducers, mostly owing to their universal application. Magnetodiodes

drawbacks of magnetodiodes via the use of the differential approach. Two-dimensional (2-D) SOS vector magnetometers frne from cross-sensitivity have been developed and

are two-terminal

galvanomagnetic elements the operation of

which is based on the superposition of high carrier injection

investigated.

by one or two junctions, magneto-concentration and surfxe recombination bus

[l-5]. These sensors have been made of var-

semiconductors,

including

gertnanium.

silicon

and

&As. At first the difference in the surface recombination velocity was achieved by polishing 2nd etching one side and

2. SOS difkewntial magnetodiodes: device structures and opentim

grinding the other. The new trend in the development of micromagnetodiodes has been silicon-on-sapphire (SOS) IC

The highly non-linear and temperature-dependent output chxacteristic I(B)

or V(B)

of magnetodiodes has led to the

technology. Owing to the crystal defects of a Si-Al,4 inter.. face. the recombinstion ve!ocity there is high, whereas on the opposite Si-SiO, interface, it is very small. The recombina-

idea of differential-magnetodiMle-b&~ microdevices. This conception is based on two facts of principal importance. the

tion rates S, on the Si-SiO,

first on- being the odd dependence of the current f(B)

intetface and S, on the Si-A&O,

or the

interface differ by a factor of lo?, i.e.. SJS, = IO’. This

vcltage V;(B) on the sign of the magnetic field B when the

unique spxilicity of the SQS syrzm naturally determiner the maximal manifestationof the magnetodiodeeffect. Under

rates S, and S, of surface recombination upon two oppxite

the action of the Lorentz force, the voltage-current characteristic of a micromagwlodiode is very sensitive lo ri mag-

condition S, B S, or S, Q: S,. It is worth noting that in this case there is an interval of magnetic fields -8,s B < + B, that includes the point B=O und within which the depend-

netic field, whxeby exceeds that of Ml

the trnnsducing efficiency substantially &vices given n wnilar signal-to-noise

ratio. The main drawbacks of the two-:emtinal todiodes. limiting

SOS magne-

their applications in control systems, are

sidewa!ls of the device with two injecting contacw fulfil the

cuciesl(B)

or V(B) arentonotonlcally

ing functions of B, i.e., I(5)

or V(B)

increasingordecreasare w’d functions of

8. In the general case these curves can be ap,xoximated by linear functions in the neighbourhood of point Bn=O, i.e., I(B) -B l-51. ‘I%erefore the purpose is to extend the interval of values of the magnetic field within which the magne-

I

tcdiode has a linear and odd output the way Hall senms have. ‘llte second facl concerns the well-known differential circuits. Their basic property is that if wo independenrfunctions Y,=Y,+~(x) aud -~a=- - ye+,‘Ix) have opposite behaviour, the overall dependence y=y, -yl cart be approximated by a linear function. The most rtnportattt advantages of differential circuits are: (a) suppression of extemll parasitic inBuences. such as teeqzrature and supply-volt.~ge fluctuations; (b) mutual compensatio:t (subtraction) of the initial vatues ye of tbe two signals; (c) odd and linear outr,ut characteristics; (d) sensitivity increase by a factor of two. The essence of the dtfferential approach to the design of magnelodicdc sensors is the development ofdevice structures whose output signal ts linear and odd with respect to point Be=0 in a relatively wide rang.5 of values of the magnetic ficldll. Since the dbection ofB is fixed while uwforminathe The II+-n-p+-n-n+

smKues_havc

been p3x.pal

on

( ICQ)

the supply current is divided’& two opposite flows. A parallel-field-activated micromagnetodiode fabricated by SOS technology is shown in Fig. I. It differs from the conventional two-tcmtinal device by its two n+-u contacts located symmetrically relative to the injecting p+-rt jtmctiort in the middle. ‘lltcn arc actually two silicon magnetodiode elements functionally integraled within a single micmstructure. Each of the two currents injected by the p+-tt junction towards the right and the left rt +-tt contacts is deflected due to the Lorentz fotce towards the respective interface (SiSiOa or Si-AllO,). That is why, depending on the polarity of the applied external magnetic field B. the coaductivi1y of one of the base regions increases (e.g.. to the left of the p+-n junction) and that of the other decreases or vice versa. Thus a differential signal A V,,(B) is gemrated across the two n+-n temtinals. llte change af the polarity of B entails a reverse polarity of AV,,tB). The inevitable offset is corupet,.ia!ed by the bimmerr (Fig. I ).

sflicou films deposiledott ( I 102) sapphii subsbws. The doping level of the n-Si film with a thickuess t-0.65 ~iisq~7X102’m-‘MdisaEhievcd~ionimpl~ of phosphorus. The optbnfzcd base length betwccrt the p+ and R+ regions is 1=30 w and the diode width is w-30 fl. We have establishedby expximeat with such diffuab tial SOS II+-a-p+-a-n+ micromsgnetodiodcs that their optimumm&e dopemtioa is the setnicoaductorregime,Bs in the case of coawntional hvMemtiaal magwtodbxks [ I+51. Our differentid SOS devices exhibit linear output characteristicsAV,(B) intherattgc - IOOmTsBs +I00 mT, the sign of AV,(B) being depndant w the polarityof B, Fig. 2. A non-linearity of less than 0.4% has been ObWWd.

Another important advantage of the differ&at approach to the desigu of magu&diode sensors is the comiderabk reduction of the temperature dependence of the output we found that with M offsel initially adjusted to be V,-0 ot T-O% its average tcmperalure drift B per T when OsSTs+WT is leas than 0.03%. S=V,(T)lOO/ A7’AV&B=O.I T)%OC-‘. Forexampk, arnagnetoswsitivityofSvn4mVmT-‘nataalc~ntofZmA(ImA in ccrh braach) was observed at T==20 “c.

3. A2DvectorsemwwitIidifftrm~SOS maguetodicda 3.1. Sfare-of-the M The implementation of more than one wtsor tiurclion of thcDctivescnsorregionisamodcnraendinthcdcvclopnent of multisensors for magxtic field, temparature and radiant flux as well as vector maguetometrxs for simultaneous or successive registration of the three mutually perpandicuhw

Ch S. Raumenin / Sense~rsand Actualors A 54 (I 996) 51~4-588

586

components of the magnetic-field vector B [ I ]. This functional approach has found application in the novel twodimensional (2-D) and three-dimensional (3-D) vector magnetometers based on different modifications of Hall sensors and magnetotransistors with orthogonal and parallelfield activation. Planar silicon technology is employed for the fabrication of sach devices [ 1,6-12]. They have the following principal advantages in comparison with discrete onecomponent galvanomagnetic devices mounted upon two or three walls of a quartz cube: (a) an extremely small volume of the transducing region and a remarkable spatial resolution, which make them very suitable for the determination of highly non-uniform (divergent) magnetic fields; (b) an optimum compatibility and better matching of the electrical, thermal and ma~netosensitivo characteristics of~he separate sensor channels; (c) improved orthogonality due to the high precisir~n of planar technology; (d) the position of the vector microsensor relative to the source of the magnetic field is not so critical as in the case of one-component magnetotransdueers. In spite of the advance of these novel and promis~ng magnetometric devices, the problem of cross-sensitivity (the influence of one of the magnetic vector compone, lts, Bx, for instance, upon the output signals of the respeeti~'e channels for By and Bz) has not found a satisfactory solution so far. The use of mieromachining is, in the author's opinion, an inventive approach that can considerably reduce the crosssensitivity of vector magnetometers due to the better separation of the active regions of their sensor ,:hannels. This technique has been successfully applied for ibe preparation of 3-D Hall sensors [ 13-15] and for mar~ufacturing 2-D CMOS BMTs where anisotropic electrocheraical etching has been introduced as a post-processing step i~t order to form a back cavity in the substrate [ 16].

p*-~l-n ÷) devices positioned at an angle of 90° with a corrimon central p*-n junction. Due to the use of an SOS process for the fabrication of this microstructure, a maximum cl~,annel resolution between the two magnetic components B~ and B~ is achieved, their oaly common region being the p ÷-n junction in the centre of the cross-like 'island'. When a magnetic field parallel to the plane of the chip is applied, it leads in the general case to the appearance of differential output signals in the two sensor channels. In thi~ way an additional gradient of the electric potential arises along each branch, which might disturb the effective symmetry of each channel initially adjusted by the trimmer r (Fig. I). Therefore the elimination of the offset is no longer guaranteed and a mechanism of cross-sensitivity appears. This drawback of the simple circuit in Fig. I can be overcome by eliminating the asymmetric bias conditions as additional sources of crosssensitivity may appear. The principal configuration of the measurement circuit for one of the channels of a 2-D SOS veetor magnetometer is shown in Fig. 4. This circuit allows the registration of the changes A I~(B) and - A It (B) via the two n +-n contacts of the channel. The two operational amplifiers A~ and A2 have high input impedances and support equal potentials at the n +-n contacts. The currents Io+AI~(B) and Io--A/2(B) generate across the resistors R2 and R3 the respective voltage drops VI =R2I ( Io + A I t ( B ) ] and V2= R3[ ( I o - A I 2 ( B ) l, w b e r e l o is the initial current when B = 0. The output differential current AL,~,(B) of one of the channels is determined by the -V Rt

3.2. 2-D SOS vector sensor free from cro ~s-sensitivity

S

Differential SOS micromagnetodiodes are the basis for tbe development of novel 2-D vector magnetometers. The layout of a 2-D SOS magnetodiode sensor tel the in-plane vector registration of magnetic fields is shown in Fig. 3. This transducer consists of two one-dirnensiona~ differential (n ~ -rl-

T o

+

n+ ~

x-out[ [

P

~ .

* .1',÷1 ° Io÷!~d

7 Fig. 3. Layoutof Ihe novel2-D SOS mal;neac-fieldvectorsensor,basedon

the magnelodiodeprinciple

D

Illml Fig, Configurationprincipleof the measurementcircuitfor one of the sensorchan~ls of the devicein Fig, 3 operatedin the current-outputmode.

Ch,S. R~4meninI 5er~gorsand Actuators A 54119~6J 584-588

40,

5~7

Kamarinos in parlioular, for ~ e i r collaboralion arid for ~ e valuable discussions.

20. fi

References

-20 -

-40

-

,p Angle (Degrees) Fig. 5. Rotational dependence of the channel output signals of a 2.D SOS vector sensor; B = 80 mT, T= 20 °C, potential difference V ~ - I/2, i.e., A V o . ~ = R A I , ~ , ( B ) when R2=Ra=R. T w o identical circuits like that in Fig, 4 are necessary for the operation o f the 2-D S O S magnetometer of Fig. 3 in the current-output mode. T h e experimental AIo~(B~) and A I , , . t ( B y ) relationships also exhibit a polar character with a good linearity inthe - 1 0 0 r o T < B < + 1 0 0 m T i m e r v a L t b e i r non-linearity factor being about 0.4%. The magnetosensitivit)' o f each channel is about 0.46 p,A r o T - ~ with a consumed power o f 50 m W at T = 2 0 °C. In order to explore the behaviour of a 2-D vector sensor which is subjected to in-plane magnetic field, experiments were performed with a rotatable pair of field coils with the micromaguetodiode device centred on the axis of rotation. Each pair o f u + - n contacts correspouding to the x- or the ychannel, is connected to a signal-processing circuit (Fig. 4 ) . Fig. 5 represents the output characteristics Ap,,~ and Al~o~ as a function of the angle o f rotation ,p of a 2-D S O S magnetometar at B ffi const. The offset of each channel has been cancelled in advance. It can be seen from the Figure that the two output currents are out o f phase by 90 °. No crosssensitivity was observed experimentally. The magnitude of the in-plane vector B is giveu by the familiar formula IB[ = (B~ 2 + B , .-.)~2

4. C o n c l u s i o n s T h e differential approach suggested for use in the building o f magnelodiodcs eliminates their two fundamental drawhacks: non-linearity and temperature dependence of the output. The new differential S O S 2-D magnetometers have high resolution aud are free from cross-sensitivity.

[ I I Ch.S. Roememn, Solid State Magnetic" Se~ors, Elsevier Science. Amsterdam. 1994. p. 434. Ch. 5 aP.dCh. ft. |2] S. Middelhock and S.A. AudeL Silicon S¢gsors, Acaden~e Press, London. 1989, p. 376. Ch. 5. [ 3 ] S. Cnstolovean u. L'effet magnetodi~e el son applic~ion aex ca~e,.n~ magn~tiques de hnute sensibilitY. L'onde dlec:rigue. 59(5) (1979) 68-74. [41 A Mohafihegh, S, CtistoJoveanu ~ d J de Pnnteh~rr'4, Doub~injection phenomena under magnetic field in SOS filn'~: a new

generation of magnetost:nsaive microdevices. IEE~ Trar~. Electron Devices, ED-28 (3) ( 1981 ) 237-242, [ 51 A. Chovet and S. Cmtoloveanu. Bases physiques el perfm'rnancesdes nouveaux (micro) captem~ mag~aques ~,scn~co~lucteur. Rev.Pky.v. AFpI.. 19 ( 1984} 69-76, [6] V. Ziesen and B.P.M. Doyndem, Magnelic-fiekl-sensitive multicollector npn-transistots, IEEE Trarz~. Electron Devices. ED-29 (1982) 83-90. 17] V. Zieren and S, Middelhoek. Mi~gnellc-field vecto¢ sensor based on a IwO-calleclortransistor lnllct ull~, Se~ors aRdAct~tors. 2 (1982) 251-261. [8] S. Kordi~, Integzmed 2-D nmgneiic sensor based on an n-p--n transistor, IEEE Electron Device Leu.. EDL-7 (1986) 196-198. [9] S. Kotdi~ and EJ.A. Munter. Integrated 3-D magnetic sensor, IEEE Trans. Electron Devices. ED-35 (1988) 771-7"/9, [10] K. Maenaka, T. Ohgusu. M, lshide and T. Nakamura, lr~egi-~ magnetic sensors detecungx, y and z components of the magnetic field, Tacit Digest, 4rh Int. Conf. Solid-Slate Sensors and Actuators ¢Tra~utucers '87), Tokyo, Japan. 3-5 Jura. 1987. pp. 523-526. [ I I ] L. Zongsheng. W. Tianping and Wu GuanglioA new integr~ed JFET 3-D nkagnetic-field sensor in VIP technology, Sensors and Actuators A, 35 t19931213-216. [ 12l Lj. RisaE. M.T. Doon and M. Paranjap ~ ~ D magnetic field sensor lealized ~ ~l lateral magnetotransislO¢in CMOS technology, Sett~lrs and Actuators. A21-A23 (1990) 770-775. [ 13] Lj. Risti~and M. Paranjape, Hall devices for multidimensional sensing of magl~fic field, Sure,ors Mater.. 5 (5) ( 19941 301-316. [141 M Par~jape. L Faancvsky and Lj. Risti6, A 3-D vertical Hal( magnetic-field sensor in CMOS technology, Ser~ors and Acmaw ,~ A, 34 (1992) 9-14. [ 15] S, Kawahito. S.O. Chat. M. Ishido 0~ndT. Nakamura, Tech. Digest. 7th Int. Cant Solid-State Sensors and Actualors (Transducers "93)+ Yokohama. Japan. 7-10 June. 1993. pp. 892-895. [ 16l C. Riccobene. K. Garmer. G. Wachnthn. H. Babes and W. Fichtner. Full three-dimensional nun.,edeal analysis of multi-ca(lector m a g n e l ~ i s l o ~ with ~irectional sensitivity. Sensors and Actgarors A. 46-.47 (1995) 289-293.

Biography Acknowledgements The author would like to thank the sensor group from Grenoble (France) and S. Cristoloveanu, A. Chovet and G.

C h a v d a r Roumenln was born in 1949 in Sofia. In 1975 he graduated from the Physics Department o f M o s c o w State University (Russia). In 1977 he acquired his Ph.D. degree

588

Ch.$. Roumenin /Sensors and Actaators A 54 (1996)584-588

L.-~galvanumagnetic properties of InSb and in 1995 his Doctor of Science degree. He is currently a professor of sensors and sensor electronics at the Institute of Control and System Research, Bulgarian Academy of Sciences. Dr Roumenin has published over 100 papers, one book and over 40 patents on

novel semiconductor magnetic sensors. He has been distinguished by the title Emeritus Inventor of Bulgaria. He is a member of the Eurosensors Steering Committee, the National coordinator of MST NEXUSPAN for Bulgaria and a Leader of the Union of Inventors of Bulgaria.