A novel 3-D Hall magnetometer using subsequent measurement method

Sensors and Actuators A 153 (2009) 205–211

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Sensors and Actuators A: Physical journal homepage: www.elsevier.com/locate/sna

A novel 3-D Hall magnetometer using subsequent measurement method S. Lozanova, Sv. Noykov, Ch. Roumenin ∗ Institute of Control and System Research - Bulgarian Academy of Science, Block 2, Acad. G. Bontchev St., Sofia 1113, Bulgaria

a r t i c l e

i n f o

Article history: Received 17 December 2008 Received in revised form 2 April 2009 Accepted 15 May 2009 Available online 28 May 2009 Keywords: 3-D Hall sensing Subsequent measurement method Magnetic-field instrumentation

a b s t r a c t A novel 3-D Hall instrument using subsequent measurement method for spatial magnetic-field components is presented. The magnetometer includes unique n-Si sensor region with square geometry (80 ␮m × 80 ␮m active area) and four corner planar contacts only, and interface circuitry which contains power supply and original signal extraction and conditioning unit with offset compensation. Three alternating combinations of electrodes provide information for the full magnetic vector at the same spot. A prototype generates in-plane channel sensitivity, Sx = Sy = 27 V/AT (27 mV/T at supply current 1 mA), and perpendicular-to-the-chip-surface sensitivity, Sz = 36 V/AT (36 mV/T at supply current 1 mA). The interface circuitry provides 2 mA stable supply current for the microdevice, and ensures obtaining of amplified, stable and offset-compensated output voltages in range [−5 V; 5 V] corresponding to the measured components of the magnetic field. The instrument ensures measurement of full magnetic-field vector with frequency 10,000 Hz. © 2009 Elsevier B.V. All rights reserved.

1. Introduction Since the magnetic field B is a vector quantity, the measurement of its three orthogonal components by one and the same sensor region is one of the most topical problems of magnetic microsystems [1,2]. This approach provides advantages that cannot be achieved by other methods: possibility to achieve very high spatial resolution—registration of fields Bx , By and Bz “at a spot”; drastically improved orthogonality between the axes, because of the precision of silicon integrated fabrication; the position of the multidimensional device with respect to the magnetic source is not as critical as in the case of 1-D sensor; electrical, thermal and galvanomagnetic matching of the individual channels; simplified bonding-wire attachment, etc. [3]. To date there are many designs of integrated silicon 2-D and 3-D magnetometers, based on the Hall effect, magnetodiodes and magnetotransistors, which have been reported, tested and commercially adopted [4–13]. The most advanced 3-D vector instruments, measuring simultaneously the components Bx , By and Bz are those using the Hall effect principle, since their action involves only one well defined and studied physical phenomenon [5–7,10]. These magnetometers, irrespective of the pronounced progress in improvement of sensor characteristics [5–13], feature some essential drawbacks. They contain quite many contacts; for example, one of the widespread 3-D microsensor solutions requires 8 electrodes [6], while a similar one requires even 13 [13]. This seriously complicates technology fabrication,

∗ Corresponding author. Tel.: +359 2 873 78 22; fax: +359 2 873 78 22. E-mail address: [email protected] (Ch. Roumenin). 0924-4247/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2009.05.017

impedes high spatial resolution and obstructs the achievement of the required miniaturization degree. This paper presents a novel designed and tested 3-D silicon vector microdevice with four contacts only, using subsequent measurement method. For the purpose, unique circuitries for offset compensation and signal conditioning have been suggested as well. At this stage, the instrument is a hybrid development in which the above-mentioned drawbacks have been overcome successfully. 2. Measurement method and device design In our opinion, the subsequent measurement procedure is a very promising approach in multidimensional magnetometry. A determining requirement is the stability of the sensor’s electric and galvanomagnetic characteristics, which is related with the perfection of the used technological processes. Most important, the measurement action is expended in time and not in space as in the simultaneous obtaining of data for the magnetic-field components. This subsequent method uses the same device, i.e. the same transducer zone, but at a different time. If we keep the data registration interval ı short enough and if the measurement repetition frequency is sufficiently high, the change of the value and the direction of the magnetic field B, the components Bx , By and Bz respectively, will be negligible with very high degree of accuracy. Therefore, in first approximation, the used subsequent method is time-independent. Moreover, under these conditions, the measurements are not influenced by the slow temperature variation of the channel magnetosensitivity and the offset. By its nature, this approach is an all-IC solution which does not result in complication of the device design and increase of the number of sensor contacts.

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3. Sensor operation principle The new vector multisensor operates in the following way [15]. The in-plane Bx measurement uses supply current lC1,4 , Fig. 1(a). The deep of the current flow in the silicon substrate is approximately 50 ␮m. The Lorentz deflections of the vertical-to-the-surface velocity components vz and −vz of electrons corresponding to currents IC1 and −IC4 are opposite ±F L = ±qvz Bx , obviously IC1 = IC4 . Hence, on contacts C2 and C3 , Hall voltage VC2,3 (Bx ) is generated [5,7,8,10,13]. The horizontal current paths, i.e. the velocity component vx , are insensitive to the y-axis Lorentz force FL , since vx and Bx are parallel. The next measurement step for the field By utilizes the velocity component vz , i.e. the current IC1,2 , while the Hall voltage is VC3,4 (By ), Fig. 1(b). The operation of the By parallel-field sensor is the same as for field Bx . The x-axis Lorentz deflections of the verticalto-the-top-surface current components IC1 and IC2 have opposite directions. Due to this effect, on output contacts C3 and C4 , Hall voltage VC3,4 (By ) is obtained. The last step of the algorithm performs the Bz measurement with velocity component v in the plane x–y, i.e. the current IC1,3 , which is perpendicular to the field Bz [5,7,14]. Output voltage VC2,4 (Bz ) is generated between terminals C2 and C4 , Fig. 1(c). In this case, the horizontal component of IC1,3 is laterally deflected in plane x–y by the Lorentz force FL . Due to the symmetry of the device structure, if for a given direction of Bx , IC2,3 is used as a biasing current at IC2,3 = IC1,4 , the respective magnetic response −VC1,4 (Bx ) will be of equal value but opposite sign to the Hall voltage VC2,3 (Bx ), Fig. 1(a). The offsets VC2,3 (0) and VC1,4 (0) are of almost equal value and the same sign, since both identical Hall devices are merged to form subsequently in time a double-Hall sensor for one and the same magnetic-field component. If as an output signal Vx (Bx ), the difference Vx (Bx ) = VC2,3 (Bx ) + VC2,3 (0) − (−VC1,4 (Bx ) + VC1,4 (0)) is used, the output will be doubled, similarly to the parallel-field Hall element suggested in [16]. The residual offset is expected to be extremely low and its thermal drift will be negligible. This procedure is utilized for the two other components By and Bz .

4. Experiments

Fig. 1. Sensor design of a new 3-D silicon four-contact Hall device: (a) measurement principle for the Bx -component; (b) measurement principle for the By -component; (c) measurement principle for the Bz -component. The dotted lines represent the Lorentz deflections of the Bx , By , or Bz component correspondently.

The novel 3-D sensor design consists of a square n-Si structure with four n+ -contacts, C1 , C2 , C3 and C4 , positioned at the top surface, near to the four corners, Fig. 1(a). These electrodes operate subsequently, according to the algorithm described below, as input and output of the microdevice for the three individual magneticfield components. The distances lC1,2 , lC2,3 , lC3,4 and lC4,1 are equal. Similar square device topology is used for the commercially available epitaxial IC Hall sensors with orthogonal magnetic field B activation [14].

The active transducing zone of the 3-D Hall device is isolated from the rest of the n-Si substrate by a deep lateral p-well. The technological implementation of the sensor is simplified and requires the well-known 4 steps for: n+ regions, p-well, metallization for electrical and bonding sheet regions and apertures in the SiO2 layer for respective metallization to n+ –n junctions. The donor concentration of the low-doped n− substrate is n = ND ≈ 1015 cm−3 . The optimized prototype with effective dimensions of the active area 80 ␮m × 80 ␮m has channel current-related sensitivities Sx = Sy ≈ 27 V/AT and Sz ≈ 36 V/AT, respectively. The absolute magnetosensitivities SA for the three channels at a supply current 1 mA are SAx = SAy = 27 mV/T and SAz = 36 mV/T, respectively. The rated current of the microdevice, IC1,4 = IC1,2 = IC1,3 , is Is = 2 mA. The output characteristics Vout (B) of the three channels are shown in Fig. 2. The overall error of magnetic induction measurement is no more than 1%. The characteristics for the Bx and By channels have very similar behaviour which is a result of the identical measurement sensor configurations The obtained non-linearity for each channel is no more than NL ≤ 0.2% at magnetic induction range B ≤ ± 0.3 T. The 3D microdevice is tested in the temperature range −20 ≤ T ≤ 100 ◦ C using a ceramic packaging. In this operating interval the obtained temperature coefficient of magnetosensitivity for the three

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Fig. 2. Sensor output characteristics of the 3-D device.

channels is T.C. = 0.1%/◦ C. The noise spectral density in the range f ≤ 1 kHz for the all channels is of the 1/f type. The noise level for the in-plane Bx and By channels is lower with respect to the known-sofar multidimensional Hall effect solutions. It is due to the fact that the sensing contacts are located outside the current-flow region, similarly to the devices suggested in [13,17–19]. The registered frequency response to ac magnetic field is greater than 40 kHz. The channel cross-sensitivity C.S. between the three axes is determined by the procedure described in [13]. The results at magnetic induction B ≤ 1.0 T are presented in Fig. 3. In our case we suppose that the vertical and lateral microdevice resolutions are no more than the geometrical sizes of the transducer region, i.e. 80 ␮m × 80 ␮m and approximately 50 ␮m, respectively. The cross-sensitivity here is no more than IC.S.I ≤ 1.6% which is mainly due to the specific current distribution in the transducer zone and the inevitable influence of the quadratic magnetoresistance. The residual channel-offsets and their temperature drifts for the operation of a double-Hall sensor are, respectively, at least 120 and 140 times smaller than these of the single-channel device. 5. Interface circuitry The signal-processing electronics is of special importance for the novel 3-D device. According to the application used, in our case substance characterization in particular biosensor systems based on magnetic nanoparticles to detect the presence of certain complexes (e.g. disease markers), the necessary rate of the measurement of full magnetic-field vector is about 10,000 Hz. The nominal supply currents of the microdevice are IC1,4 = IC1,2 = IC1,3 = IC2,3 = IC4,3 = IC2,4 = 2 mA. The resistances between the terminals of the microdevice RC1,4 , RC1,2 , RC1,3 , RC2,3 , RC4,3 , RC2,4 are no more than 2 k. Switching measurements of the microdevice sample show that the Hall voltage will be valid only after ≈1000 nS have elapsed from the plate commutation transition. The working range of the microdevice is 1 ≤ B ≤ 1000 mT. The in-plane channel-magnetosensitivity Sx = Sy = 27 V/AT and the perpendicu-

Fig. 3. Cross-sensitivity between the three axes at supply current Is = 2 mA and T = 20 ◦ C.

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lar one Sz = 36 V/AT. Therefore, the output microdevice signals Vin (which are input signals for the signal-interface circuit) may vary from 54 ␮V to 72 mV. The aim is to develop a convenient supply and output interface circuitry which should provide amplified, stable and offsetcompensated voltages corresponding to the measured components of the magnetic field Bx , By and Bz . These voltages should be in range [−5 V; 5 V]. Based on the above listed technical data and requirements, the period tfull = 100 ␮S for the measurement of the full vector of the magnetic induction is chosen. This way, the rate of the measurement of the full vector of the magnetic induction is 10,000 Hz, which satisfy the above presented requirement to measure it with rate at least 10,000 times per second. Therefore, the measurement for each of the components of the magnetic field Bx , By or Bz should take tone component = tfull /3 ≈ 33.4 ␮S. As is described in the end of Section 2, for the purpose of offset reduction, two single measurements are required to obtain each of the voltages Vx (Bx ), Vy (By ), and Vz (Bz ), namely: VC2,3 (Bx ) and VC1,4 (Bx ) for Vx (Bx ); VC4,3 (By ) and VC1,2 (By ), for Vy (By ); VC2,4 (Bz ) and VC1,3 (Bz ) for Vz (Bz ). Thus, the measurement process for each of the voltages Vx (Bx ), Vy (By ), and Vz (Bz ) consists of 2 states—first and second. Therefore, the single measurement should take tsingle = tone component /2 ≈ 16.7 ␮S. Hence, the rate of the single measurements should be at least f = 1/tsingle ≈ 60,000 Hz. Due to the relatively low working frequency, it is preferable to use CMOS IC as constructive components for the interface circuitries. They are relatively low-cost and characterized by high noise immunity and low static power consumption. In this stage for the processing circuits realization is used hybrid approach. The block diagram of the sensor interface circuit is shown in Fig. 4. The schematic diagram of the of the sensor interface circuit is shown in Fig. 5. The Block 1, “Pulse Generator” (formed by U1, R1 , R2 , C1 , C2 in Fig. 5), clocks the mod-6 counter (Block 2) by pulse sequence with frequency f = 62,300 Hz. The Block 2 (formed by U2 in Fig. 5) generates a sequence for control of: (1) the switching over the terminals of the microdevice (Block 4) to the power supply circuit current source (Block 6); (2) the switching over the terminals of the microdevice (Block 4) to the amplifier of the multiplexed signal (Block 8); and (3) for control of the Block 9, “Six sample-and-hold with multiplexed input”. Based on this control sequence, the Block 5, “Analog Demultiplexer” (formed by U6 in Fig. 5), directly switches over the current source (Block 5) to the device (denoted as Block 4 in Fig. 4, and as U8 in Fig. 5) terminals C1 –C4 , C2 –C3 , C1 –C2 , C4 –C3 , C1 –C3 , C2 –C4 consecutively, in order to ensure the measurement of the Hall voltages VC2,3 (Bx ), VC1,4 (Bx ), VC4,3 (By ), VC1,2 (By ), VC2,4 (Bz ), VC1,3 (Bz ). In accordance with the technical data and requirements, the current source, formed by U7, R5 , R6 and C5 in Fig. 5, should be able to support stable supply current ISOURCE = 2 mA through each of the supply loops of the microdevice with resistances RC1,4 , RC1,2 , RC1,3 , RC2,3 , RC4,3 , RC2,4 ≤ 2 k. The error in accurately setting ISOURCE with this composite configuration is derived from three sources. VREF , R5 , and R6 are available in 0.1% or 0.2% tolerance. U7’s ground-current variation of ±15 ␮A on 30 ␮A translates to an additional 0.75% tolerance. When these tolerances are combined, the total ISOURCE tolerance is smaller than 1.5%. Similarly, ISOURCE ’s insensitivity to temperatures from −40 to 85 ◦ C is a function of the temperature coefficients of VREF , R5 , R6 , and IC1’s ground current. The REF195 is available in a 0.1% tolerance with 20 ppm/◦ C TC grade. Inexpensive resistors are commonly available in 0.1% tolerance with 25 ppm/◦ C TC grade. The REF195’s ground-current variation of ±2 ␮A on 30 ␮A over temperature provides an additional TC of 20 ppm/◦ C. Therefore, the total ISOURCE TC is lower than 50 ppm/◦ C. The block 7, “Analog Multiplexer” (formed by U3 in Fig. 5), controlled by the Block 2 output signal, collects the Hall voltages

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Fig. 4. The block diagram of the sensor interface circuitry.

VC2,3 (Bx ), VC1,4 (Bx ), VC4,3 (By ), VC1,2 (By ), VC2,4 (Bz ), VC1,3 (Bz ) from the microdevice consecutively, and passes them to the Block 8, “Amplifier of the multiplexed signal” as alternating consequence VC2,3 (Bx ), VC1,4 (Bx ), VC4,3 (By ), VC1,2 (By ), VC2,4 (Bz ), VC1,3 (Bz ). In both Blocks 5 and 7, a CMOS analog multiplexer/demultiplexer may be used, like ADG407. The ADG407, with its low on resistance (80  max), and fast switching abilities (tON < 160 ns; tOFF < 150 ns) is proper for such application. In Block 8 (formed by U9 in Fig. 5), a precise instrumentation amplifier like AD623, AD8553, AD8230, etc., may be used. The lowcost in-amp AD623, with its single supply operation ability, high accuracy of 50 ppm maximum non-linearity, low input bias current of 25.0 nA max, 84 dB Min CMRR, and low noise, is ideal for use in precision data acquisition systems like this application. To obtain demultiplexed steady values of VC2,3 (Bx ), VC1,4 (Bx ), VC4,3 (By ), VC1,2 (By ), VC2,4 (Bz ), VC1,3 (Bz ), the multiplexed output signal of the Block 8 is passed to Block 9, “Six sample-and-hold circuits with multiplexed input”, formed by U12 in Fig. 5. The Block 3 passes to the channel addressing inputs of the Block 9 proper code, and this way a proper sample-and-hold circuit is activated in the proper moment. For this particular application, the CMOS Octal Sampleand-Hold Amplifier SMP 08 matches very well the requirements for

the sample-and-hold circuits in Block 9. The SMP08 is a monolithic octal sample-and-hold; it has eight internal buffer amplifiers, input multiplexer, and internal hold capacitors. It is manufactured in an advanced oxide isolated CMOS technology to obtain high accuracy, low droop rate (max 20 mV/s), and fast acquisition time. The SMP08 has a typical linearity error of only 0.01% and can accurately acquire a 10-bit input signal to ±1/2 LSB in less than 7 ␮s. The Block 3, “Pulse former circuit”, formed by U4, U5, R3 , R4 , C3 , C4 in Fig. 5, is intended to form proper narrow pulses for clocking the sample-and-hold circuits in Block 9. The obtained demultiplexed steady values of VC2,3 (Bx ), VC1,4 (Bx ), VC4,3 (By ), VC1,2 (By ), VC2,4 (Bz ), VC1,3 (Bz ) are passed to three differential amplifiers as is shown in Fig. 4: VC2,3 (Bx ) and VC1,4 (Bx ) to Block 10a “Differential amplifier x”, formed by U14 in Fig. 5; VC4,3 (By ) and VC1,2 (By ) to Block 10b “Differential amplifier y”, formed by U15 in Fig. 5; VC2,4 (Bz ) and VC1,3 (Bz ) to Block 10c “Differential amplifier z”, formed by U13 in Fig. 5. The outputs of these differential amplifiers give the steady and offset-compensated values of Vx (Bx ), Vy (By ), and Vz (Bz ), as is shown in Fig. 4. The commutations of the different signals in the signal-interface circuit in accordance with the Block 2 (Mod-6 counter) control outputs are presented in Table 1.

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Fig. 5. The schematic diagram of the sensor interface: (a) the pulse generator, mod-6 counter, current source, analog demultiplexer, analog multiplexer, pulse former circuit; (b) the precise instrumentation amplifier, six sample-and-hold circuits with multiplexed input, differential amplifier x, differential amplifier y, differential amplifier z.

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Table 1 The commutations of the different signals in the signal-interface circuit in accordance with the Block 2 (Mod-6 counter) control outputs, see also Figs. 4 and 5. Block 2 (Mod-6 counter) outputs

Measured Hall voltage

State

Hall sensor contacts, switched to Block 6 (current source)

Hall sensor contacts, switched to Block 8 (diff. amplifier of the multiplexed signal)

Addressed channel of Block 9 (octal sample- and-hold with multiplexed input)

000 001

Vx (Bx )

First Second

C1 –C4 C2 –C3

C2 –C3 C1 –C4

CH0 CH1

010 011

Vy (By )

First Second

C1 –C2 C4 –C3

C4 –C3 C1 –C2

CH2 CH3

100 101

Vz (Bz )

First Second

C1 –C3 C2 –C4

C2 –C4 C1 –C3

CH4 CH5

The simplified timing diagram which illustrates forming of narrow pulses for clocking the sample-and-hold circuits in Block 9, is presented in Fig. 6. With the described above arrangement, when measuring each of the components of the magnetic field Bx , By and Bz , at each change of state (from first to second), the measured Hall voltage VCi,j (Bk ) changes polarity and the corresponding offset voltage VCi,j (0) remains quasi-constant. The indexes i and j denote the numbers of the measured output contacts of the microdevice at the moment (i, j = 1,2,3, or 4), and index k denotes the measured component of the magnetic field at the moment (x, y, or z). This way, the dc input-referred offset VOA of the amplifier of multiplexed signal U9, will become indistinguishable from the offset voltage VCi,j (0), and the microdevice and the input amplifier offsets will be simultaneously processed and cancelled. Thus, the U9 offset is cancelled at no cost, avoiding the extra hardware required to perform the same function by other techniques. Here we borrow the basic idea for cancellation of two indistinguishable offsets from [20]. The principle of the offset cancellation technique is as follows. For the first component Bx of the magnetic induction, directed to

axle X, the sensor generates the following input voltages to the ideal amplifier U9: Vx (Bx )2,3 = VC2,3 (Bx ) + VC2,3 (0) during first state Vx (Bx )1,4 = −VC1,4 (Bx ) + VC1,4 (0) during second state

(1)

Assuming ideal S/H functions, the output signals CH0OUT and CH1OUT of U12 for the signal Vx (Bx ) become Vx (Bx )2,3 , U12 = G1 [VC2,3 (Bx ) + VC2,3 (0) + VOA ] during first state (2) Vx (Bx )1,4 , U12 = G1 [−VC1,4 (Bx ) + VC1,4 (0) + VOA ] during second state where G1 is the gain of the U9. Subtracting these two dc voltages by means of the differential amplifier U14 with gain G2 produces, neglecting U14 offset contributions, the output Vx (Bx ) = G1 G2 (VC2,3 (Bx ) + VC1,4 (Bx )) + G1 G2 Vres (0)

(3)

where Vres (0) = VC2,3 (0) − VC1,4 (0) is so-called residual microdevice offset [20] which is extremely low and its thermal drift is negligible. By analogy, the results for Vy (By ) and Vz (Bz ) can be obtained. The gains of the amplifiers U9, U13, U14, and U15 are set to be adjustable: they may vary from 2 to 1000. This results from the fol-

Fig. 6. The simplified timing diagram which illustrates the formation of narrow pulses for clocking the sample-and-hold circuits.

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lowing reasons. The sensor’s sensitivities along the different axes are different. In order to calculate the components/magnitude of the field properly, it is necessary to adjust the gain of each channel in accordance with the corresponding sensitivity. Moreover, depending on the fabrication process, crystallographic orientation, and dimensions of the active sensor field, the expected value of the offset voltages VCi,j (0) may range from several tens ␮V to several tens mV for supply current 2 mA. For smaller offset values VCi,j (0), in order to minimize the influence of the offset contributions of U13, U14 and U15, it is preferable to increase the gain of U9, and decrease the gains of U13, U14, and U15. For larger offset values VCi,j (0), in order to avoid driving U9 into saturation, it is preferable to decrease the gain of U9, and increase the gains of U13, U14, and U15. This way, for the full range of input signals |Vin | (from 54 ␮V to 72 mV), the output signals could be fixed in range Vout ∈ [−5 V; 5 V]. The obtained steady and offset-compensated values of Vx (Bx ), Vy (By ), and Vz (Bz ) may be passed to an analog or digital computational unit (Block 11 in Fig. 4). The induction value of Bx , By or Bz component is given by the expression B = VH /SA , where SA is the respective absolute channel magnetosensitivity. The magnitude of the vector B is obtained by the familiar formula |B| = 1/2

(Bx2 + By2 + Bz2 ) . One proper realization of such kind analog computational unit is presented in [14]. Here, the amplified signals Vi (Bi ) are squared using the Gilbert multiplier circuit, and the square root operation is performed using the translinear technique. 6. Conclusions The new triaxial Hall magnetometer based on a subsequent magnetic-field component measurement principle has only four contacts; very small dimensions, which provide high spatial resolution; strongly reduced noise, offsets and offset temperature drifts; small non-linearity and channel cross-sensitivity suitable for many precise measurement applications, etc. The original interface circuitry for the supply and for the output signal extraction is very promising. The proposed 3-D Hall device for subsequent measurement with minimal design complexity is the most simplified of all known-so-far multidimensional magnetic microsensors. The potential applications of the new 3-D Hall device are in the low-field magnetometry, position sensors, angular displacement detection, angle decoder, the motion control, automobile industry including ABS systems, etc. References [1] L. Latorre, P. Nouet, A complete methodology for electro-mechanical characterization of a CMOS compatible MEMS technology, IEICE Trans. Electron. E82-C (4) (1999) 582–588. [2] K. Maenaka, Y. Shimizu, M. Baba, M. Maeda, Application of multidimensional magnetic sensors—position and movement detection, Sensors Mater. 8 (1) (1996) 33–46. [3] Ch. Roumenin, D. Nikolov, I. Icanov, Amperometric circuit for high accuracy 2D and 3D magnetic-field measurements, Meas. Sci. Technol. 14 (2003) 851– 857.

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[4] A. Haberli, M. Schneider, P. Malcovati, R. Castagnetti, F. Maloberti, H. Baltes, Two-dimensional magnetic microsensor with on-chip signal processing for contactless angle measurement, IEEE J. Solid-State Circ. 31 (12) (1996) 1902–1907. [5] C. Roumenin, Solid State Magnetic Sensors, Elsevier, 1994. [6] C. Schott, F. Burger, H. Blanchar, L. Chiesi, Modern integrated silicon Hall sensors, Sensor Rev. 18 (4) (1998) 252–257. [7] Ch.S. Roumenin, in: J.G. Korvink, O. Paul (Eds.), MEMS—A Practical Guide To Design, Analysis and Applications, William Andrew Publ, USA, 2006. [8] S. Middelhoek, S. Audet, Silicon Sensors, Acad. Press, London, 1989. [9] P. Ripka (Ed.), Magnetic Sensors and Magnetometers, Artech, London, 2001. [10] M. Paranjape, I. Filanovski, A 3-D vertical Hall magnetic-field sensor in CMOS technology, Sensors Actuators A 34 (1992) 9–14. [11] H.-Yi. Lin, T. Fu Lei, Jz-Jan Jeng, C-Ling Pan, C.-Yen Chang, A novel structure for three-dimensional silicon magnetic transducers to improve the sensitivity symmetry, Sensors Actuators A 56 (1996) 233–237. [12] O. Yilmazoglu, M. Brandt, J. Sigmund, E. Genc, H.L. Hartnagel, Integrated InAs/GaSb 3D magnetic field sensors for the intelligent tire, Sensors Actuators A 94 (2001) 56–63. [13] Ch.S. Roumenin, D. Nikolov, A. Ivanov, 3-D silicon vector sensor based on a novel parallel-field Hall microdevice, Sensors Actuators A 110 (2004) 219–227. [14] T. Nakamura, K. Maenaka, Integrated magnetic sensors, Sensors Actuators A 21–23 (1990) 762–769. [15] S. Lozanova, Ch. Roumenin, Silicon four-contact Hall microdevice for subsequent 3-D magnetic field measurement, in: Book of Abstr. of Eurosensors XXII Conf., Drezden, Germany, 2008, p. 88. [16] R. Steiner, Rotary Switch and Current Monitor by Hall-based Microsystems, PEL-ETH Publ, Switzerland, 1999. [17] Ch. Roumenin, A. Ivanov, Hall microsensor, Bulg. Patent BG 64492 B1/12.07.2001. [18] Ch. Roumenin, D. Nikolov, A. Ivanov, A novel parallel-field Hall microsensor, in: Proc. of the 16 Europ. Conf. on Solid-State Transducers—Eurosensors XVI, Czech Rep., 2002, pp. 545–548. [19] J. Pascal, L. Hebrard, J.-B. Kammerer, V. Frick, J.-P. Blonde, First vertical Hall device in standard 0.35 ␮m CMOS technology, Sensors Actuators A (2008), doi: 10.1016/j.sna.2008.03.011. [20] A. Bilotti, G. Monreal, R. Vig, Monolithic magnetic Hall sensor using dynamic quadrature offset cancellation, IEEE J. Solid-State Circuits 32 (6) (1997) 829–836.

Biographies Siya Lozanova has received Master’s degree in automation and electronics from Technical University, Sofia, Bulgaria in 1996. Since the same year, she has been working as research associate at the Institute of Control and System Research of the Bulgarian Academy of Sciences. She is working in the field of sensor systems, magnetic field microdevices as magnetotransistors, magnetodiodes, Hall effect elements, etc. She has received PhD degree on magnetic field sensors in 2006. Dr. S. Lozanova is coordinator for Bulgaria of 6 FP Project MINAEAST-NET. Svetoslav Noykov received the MSc degree in electromechanical engineering from Tula State University, Russia, in 1992. He developed a PhD thesis in the Institute of Control and System Research—Bulgarian Academy of Sciences, and received the PhD degree in elements and devices of the automation and the computer technique, in 2004. His current research interests include sensors devices and sensor interface electronics. Ch. S. Roumenin was born in 1949 in Sofia. In 1975 he graduated from the Physical Department of Moscow State Univ. (Russia). In 1977 he acquired his PhD degree on galvanomagnetic properties of InSb and in 1995 his full Doctor of Science degree on magnetic field sensors and microsystems and their applications. He is currently a professor of sensors and sensor electronics at the Institute of Control and System research, Bulg. Acad. Sci. Since 1999 he is Director of the ICSR. In 2004 Ch. Roumenin is elected as corresponding member of the Bulgarian Academy of Sciences. He has published over 300 papers, 3 books and over 70 patents on novel sensors and microsystems. He has been distinguished by the title Emeritus Inventor of Bulgaria and his name is entered in the Golden Book of Bulgarian Inventors in 1977. Ch. S. Roumenin is a member of the Eurosensors Intern. Steering Committee and the Editorial Board of Sensors and Actuators Journal.