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Bipolar magnetic microsensor for longitudinal fields
Sensors and Actuators A 110 (2004) 259–263
Bipolar magnetic microsensor for longitudinal fields Marioara Avram∗ , Otilia Neagoe1 , Cecilia Codreanu, Cornel Voitincu, Monica Simion National Institute for Research and Development in Microtechnologies (IMT Bucharest), Str. Erou Iancu Nicolae 32B, 72996 Bucharest, Romania Received 20 September 2002; received in revised form 15 October 2003; accepted 24 October 2003
Abstract In this paper, we introduce a novel bipolar magnetic sensor for a field parallel to surface. It is designed in standard integrated bipolar technology and it consists of a pair of identical vertical n-p-n transistors anti-symmetrically oriented, whose bases are made up of two diffusions with different depths. Each transistor practically is made up of two structures connected in parallel. The only difference between them consists in different thickness and impurity concentration within the base. High sensitivity, low offset, and high linearity over large ranges of the magnetic field induction are obtained. © 2003 Elsevier B.V. All rights reserved. Keywords: Bipolar magnetotransistors; Magnetic sensors; Integrated circuit
1. Introduction The bipolar magnetotransistors are the most widespread magnetic sensors because they have high transduction efficiency; relatively high-temperature immunity and they reject all parasitic signals, which are not associated with the action of the magnetic field [1]. As a bipolar magnetotransistor is built on a non-magnetic substrate (Si), the external magnetic field, B, influences only the kinetic processes of charge carriers in different regions of the transistor structure. The magnetic field influences the energy flowing and modulates that flow. The mechanism of magnetic control of the output collector current IC (B) is attributed to Lorenz deflection of minority carriers in the collector region. Pure Lorenz deflection of the injected carriers is the main mechanism influencing the operation of this type of bipolar magnetotransistor, due to its long base regions unconfined in the direction of the Lorenz force that eliminates the possibility of occurrence of a Hall effect. Due to the moderate levels of injection and deep collector regions, emitter injection modulation is the second mechanism occurring in a magnetotransistor. In a magnetic field parallel to the structure surface, the Hall field EH (B) is located between the vertical sides of the two deep collector regions. The field EH (B) most probably ∗
Corresponding author. Tel.: +40-21-490-8412; fax: +40-21-490-8238. E-mail address: [email protected] (M. Avram). 1 ESSEX Bucharest, Romania. 0924-4247/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2003.10.052
does not contribute to the deflection of the injected carriers, but controls electrostatically the drift–diffusion distribution of the minority carriers between collectors. Depending on its direction, the Hall field slows down minority carrier diffusion towards one of the collectors and pushes them towards the other. The related sensitivity of magnetic sensor is defined as: S(B) =
IC (B) IC (0) · B
(1)
where IC (B) is the variation of the collector current in the presence of the magnetic field, IC (0) the collector current in the absence of the magnetic field and B the magnetic induction [2]. The novelty of the present device consists in the layout design and the technological process with two differently doped bases. The magnetic field sensor bases its functionality both on the Lorenz deflection of the minority carriers in the collector region and also on the emitter injection modulation due to the moderate levels of injection and deep collector regions [3,4].
2. Operating principle Fig. 1 presents the electrical scheme of the integrated magnetotransistor. The magnetic field causes a variation of the voltage drop on the emitter–base junction and this effect in turn, results in non-uniformity of the carrier injection
260
M. Avram et al. / Sensors and Actuators A 110 (2004) 259–263
C1
3. Sensor design
C2
B1
B2
E Fig. 1. The electrical scheme of the sensor.
into the base, and subsequent unequal currents to the two collectors. The magnetic field dictates which portion of the emitter has an enhanced injection and which of the two collectors receives more current [5,6]. In a first-order approximation, the difference in base width is translated for RAN operation into the amplifying factor difference. At equilibrium, under identical bias conditions, transistors behave in the same way, and the two collector currents are theoretically equal. In the presence of a magnetic field parallel to the structure surface and perpendicular to the longitudinal axis, an interaction occurs with the electrical field in the positively biased structure (VCE = V + ), resulting in generation of an electrical field parallel to the structure longitudinal axis.
The bipolar magnetotransistor sensing magnetic fields parallel to surface is designed in standard integrated circuits bipolar technology has the layout presented in Fig. 2. It consists of a pair of identical vertical npn transistors anti-symmetrically oriented. Bases are made up of two diffusions with different depths. Each transistor is practically made up of two structures having different thickness and impurity concentrations within the base, and connected in parallel. The base is biased through a current generator and has a floating potential dictated by the emitter fixed potential and by emitter–base junction open voltage. A floating potential gradient occurs along the base due to layer resistive effect and to the Hall field. The Hall field differently affects the two halves of the structure, favouring a supplementary opening for one-half of the emitter–base junction, while the other is obstructed. The potential gradient is fixed only in the centre of the structure. Thus, because of the Hall field and of the layer resistive effect, the contact on the base is expected only in the centre of the structure. The processed structure of the bipolar lateral magnetotransistor is shown in Fig. 3.
4. Technology of fabrication The sensor is fabricated in a standard integrated circuit technology, by using an eight-mask process. Very high-quality p-type mono-crystalline silicon wafers, of resistivity ρ ≈ 7.5 cm (n0 ≈ 1015 cm−3 ) and thickness of
Fig. 2. The layout of the bipolar magnetic microsensor.
M. Avram et al. / Sensors and Actuators A 110 (2004) 259–263
261
Fig. 3. The structure of the bipolar magnetic microsensor.
approximately 350 m were used as substrate. The crystallographic orientation of wafers is (1 0 0). The first technological step involves the diffusion of a buried antimony n+ layer. This buried diffusion serves to realize the high doped region of the transistor collectors. The following high-temperature annealing (1200 ◦ C) and the subsequent high-temperature steps drive the antimony atoms 3–4 m deep into the substrate. A 12 m thick n-type epitaxial layer, 4 m thicker than the standard epitaxial layer, is grown of wafers. This epitaxial layer plus the underlying buried n+ layer will form the collector regions. The doping level of the epi-layer is approximately 6 × 1015 cm−3 . By using a proper buried n+ layer layout it is possible to create the bases. Moreover, the integrated bipolar electronics is placed in the epitaxial layer as well. To isolate different circuit elements on the chip, a p+ diffusion is carried out, the so-called p-type deep diffusion. After that, follows a phosphorus deposition and a drive-in for the n+ collector plugs. This deep n-type layer is also used for the reduction of the contact resistance to the epi-layer. After the high-temperature steps the residual oxide is stripped and a thin (1000 Å) high-quality thermal oxide is grown. Boron atoms are implanted through the oxide to form the emitter and base regions of the bipolar transistors. PECVD oxide is deposited and opened through the contact mask. A wet dip-etch is performed in order to remove completely the remaining oxide and 0.6 m thick Al/1%Si is sputtered and patterned to form the interconnects. The magnetic sensor has two buried n+ collectors separated by a small distance to eliminate the shorting effects. The epi-layer has been deposited under the collectors to enhance magnetic sensitivity. The two collectors are used as an active load of the differential preamplifier in an operational amplifier. The technological profile of the sensor can be seen in Fig. 4 that illustrates the successive technological steps (layers) for one-half of the sensor structure.
Emitter
Base Emitter Base Collector
n-Epi P+ base P+ base P N+ buried collector
P+ P substrate
Fig. 4. The technological profile of the sensor.
5. Sensor performances Fig. 5 illustrates the test set-up used for the measurements and to characterize sensor parameters.
+12V
6
+12V -12V
+5V
7
4
1
5 4
+12 2
3 1
3 + 2 +1
-12 2
B
+12
1 2 3
2
7 + -12
+ -12 3
-12V
Fig. 5. The schematic of biasing and signal conditioning circuit for the bipolar magnetotransistor.
M. Avram et al. / Sensors and Actuators A 110 (2004) 259–263
2
500
1.5
400 Offset (nA)
Magneticsensitivity (1/T)
262
1 0.5 0 0
100 200 300 400 Magnetic induction (mT)
300 200 100
500
0
Fig. 6. Magnetosensitivity variation with magnetic induction, for 2.5 mA base current.
0
0.1
0.2 0.3 0.4 Magnetic induction (T)
0.5
0.6
Magnetosensitivity (1/T)
Fig. 8. The offset variation with magnetic induction.
2.5
experimental results confirm the theoretical operating principle.
2 1.5 1 0.5
6. Conclusions
0 0
0.5
1
1.5 2 2.5 3 3.5 4 4.5 Supplied current (mA)
Fig. 7. Magnetosensitivity variation with supplied current, for a magnetic induction of 0.5 T.
All measurements are made in common base configuration. A positive voltage is applied to base from a DC voltage source VCC . The application of voltage VB between the two bases of the device causes a majority carrier current flow through the device’s active region, which leads to a certain potential distribution in the silicon substrate. The differential collector current component due to carrier deflection is a linear function of the magnetic field B, it depends on the difference of the capture area [3], and the differential collector current component due to the emitter injection modulation is an exponential function of the voltage Hall, VH : IC = IC1 − IC2 = α(IC0 , B)
VT VH /VT (e − 1)(eEH (L−1)/VT + 1) VH
(2)
To illustrate the sensor performances, we have represented the microsensor magnetosensitivity variation with the magnetic field and the supplied current in Figs. 6 and 7, respectively, and the offset current as a function of the magnetic field induction in Fig. 8. High sensitivity and low offset over large ranges of the magnetic field induction were obtained. The relative magnetosensitivity of the sensor is in the range 1–5 T−1 for measured magnetic fields less than 1 T. It increases when the supplied current in the transistor base is increased. The emitter shape, with long metal tracks, favours the offset diminution, such that the offset current is only 500 nA for measured magnetic fields up to 600 mT. The
The bipolar magnetotransistor for a surface parallel field is designed and realized in a standard integrated bipolar technology. It consists of a pair of identical vertical npn transistors anti-symmetrically oriented. Bases are made up of two diffusions with different depths. Each transistor is practically made up of two structures having different thickness and impurity concentrations within the base, and connected in parallel. High sensitivity and low offset over large ranges of the magnetic field induction are obtained.
References [1] Ch.S. Roumenin, Magnetic sensors continue to advance towards perfection, Sens. Actuators A 46–47 (1995) 273–277. [2] R. Castagnetti, M. Schneider, H. Baltes, Sens. Actuators A 46–47 (1995) 280–283. [3] R.S. Popovic, Hall Effect Devices, Adam Hilger, IOP Publishing, Bristol, England, 1991. [4] R.S. Popovic, Z. Randjelovic, D. Manic, Integrated Hall-effect magnetic sensors, Sens. Actuators A 2924 (2001) 1–5. [5] M. Avram, O. Neagoe, A new bipolar magnetotransistor with combined phenomena of carrier deflection and emitter injection modulation, in: Proceedings of the International Semiconductor Conference, Sinaia, Romania, 1996. [6] M. Avram, O. Neagoe, T. Lipan, Lateral bipolar magnetotransistors with enhanced emitter injection modulation and carrier deflection, in: Proceedings of the International Semiconductor Conference, 1997.
Biographies Marioara Avram was born in 1958 on 17th of January, in Bucharest, graduated in 1982, Faculty of Physics, University of Bucharest, and in 1990, Faculty of Automatics and Computers, “Politehnica” University of Bucharest (P.U.B.). Presently she is a senior research fellow with the National Institute for Research and Development in Microtechnologies, Bucharest, and a PhD student at the University of Bucharest. Since 1998 she is a member of the IEEE Electron Device Society. The main research interests are in the field of design and characterization of bipolar and unipolar devices, bipolar magnetotransistors, Hall sensors, and magnetic sensors based on field emission in vacuum.
M. Avram et al. / Sensors and Actuators A 110 (2004) 259–263 Cecilia Codreanu was graduated in 1972, Faculty of Electronics Engineering, “Politehnica” University of Bucharest (P.U.B.). She is currently a senior research fellow with the National Institute for Research and Development in Microtechnologies, Bucharest. The main research interests are in the field of design and characterization of BJT, JFET, MESFET transistors, and the physics of semiconductor materials: Si, GaAs, SiC. Member of the IEEE Electron Device Society.
263
Cornel Voitincu was born in 1967 on 29th of May, in Bucharest, graduated in 1992, The Electronics and Telecommunications Faculty, “Politehnica” University of Bucharest. From 1996, he is a research fellow with the National Institute for Research and Development in Microtechnologies, Bucharest. The computer assisted design (CAD) of the dipolar integrated circuits, analysis and simulation with ASIC-SPICE of electronic blocks, and schemes and interface layouts for monolitic/hibride integrated circuits are among the main research interests.
Bipolar magnetic microsensor for longitudinal fields Marioara Avram∗ , Otilia Neagoe1 , Cecilia Codreanu, Cornel Voitincu, Monica Simion National Institute for Research and Development in Microtechnologies (IMT Bucharest), Str. Erou Iancu Nicolae 32B, 72996 Bucharest, Romania Received 20 September 2002; received in revised form 15 October 2003; accepted 24 October 2003
Abstract In this paper, we introduce a novel bipolar magnetic sensor for a field parallel to surface. It is designed in standard integrated bipolar technology and it consists of a pair of identical vertical n-p-n transistors anti-symmetrically oriented, whose bases are made up of two diffusions with different depths. Each transistor practically is made up of two structures connected in parallel. The only difference between them consists in different thickness and impurity concentration within the base. High sensitivity, low offset, and high linearity over large ranges of the magnetic field induction are obtained. © 2003 Elsevier B.V. All rights reserved. Keywords: Bipolar magnetotransistors; Magnetic sensors; Integrated circuit
1. Introduction The bipolar magnetotransistors are the most widespread magnetic sensors because they have high transduction efficiency; relatively high-temperature immunity and they reject all parasitic signals, which are not associated with the action of the magnetic field [1]. As a bipolar magnetotransistor is built on a non-magnetic substrate (Si), the external magnetic field, B, influences only the kinetic processes of charge carriers in different regions of the transistor structure. The magnetic field influences the energy flowing and modulates that flow. The mechanism of magnetic control of the output collector current IC (B) is attributed to Lorenz deflection of minority carriers in the collector region. Pure Lorenz deflection of the injected carriers is the main mechanism influencing the operation of this type of bipolar magnetotransistor, due to its long base regions unconfined in the direction of the Lorenz force that eliminates the possibility of occurrence of a Hall effect. Due to the moderate levels of injection and deep collector regions, emitter injection modulation is the second mechanism occurring in a magnetotransistor. In a magnetic field parallel to the structure surface, the Hall field EH (B) is located between the vertical sides of the two deep collector regions. The field EH (B) most probably ∗
Corresponding author. Tel.: +40-21-490-8412; fax: +40-21-490-8238. E-mail address: [email protected] (M. Avram). 1 ESSEX Bucharest, Romania. 0924-4247/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2003.10.052
does not contribute to the deflection of the injected carriers, but controls electrostatically the drift–diffusion distribution of the minority carriers between collectors. Depending on its direction, the Hall field slows down minority carrier diffusion towards one of the collectors and pushes them towards the other. The related sensitivity of magnetic sensor is defined as: S(B) =
IC (B) IC (0) · B
(1)
where IC (B) is the variation of the collector current in the presence of the magnetic field, IC (0) the collector current in the absence of the magnetic field and B the magnetic induction [2]. The novelty of the present device consists in the layout design and the technological process with two differently doped bases. The magnetic field sensor bases its functionality both on the Lorenz deflection of the minority carriers in the collector region and also on the emitter injection modulation due to the moderate levels of injection and deep collector regions [3,4].
2. Operating principle Fig. 1 presents the electrical scheme of the integrated magnetotransistor. The magnetic field causes a variation of the voltage drop on the emitter–base junction and this effect in turn, results in non-uniformity of the carrier injection
260
M. Avram et al. / Sensors and Actuators A 110 (2004) 259–263
C1
3. Sensor design
C2
B1
B2
E Fig. 1. The electrical scheme of the sensor.
into the base, and subsequent unequal currents to the two collectors. The magnetic field dictates which portion of the emitter has an enhanced injection and which of the two collectors receives more current [5,6]. In a first-order approximation, the difference in base width is translated for RAN operation into the amplifying factor difference. At equilibrium, under identical bias conditions, transistors behave in the same way, and the two collector currents are theoretically equal. In the presence of a magnetic field parallel to the structure surface and perpendicular to the longitudinal axis, an interaction occurs with the electrical field in the positively biased structure (VCE = V + ), resulting in generation of an electrical field parallel to the structure longitudinal axis.
The bipolar magnetotransistor sensing magnetic fields parallel to surface is designed in standard integrated circuits bipolar technology has the layout presented in Fig. 2. It consists of a pair of identical vertical npn transistors anti-symmetrically oriented. Bases are made up of two diffusions with different depths. Each transistor is practically made up of two structures having different thickness and impurity concentrations within the base, and connected in parallel. The base is biased through a current generator and has a floating potential dictated by the emitter fixed potential and by emitter–base junction open voltage. A floating potential gradient occurs along the base due to layer resistive effect and to the Hall field. The Hall field differently affects the two halves of the structure, favouring a supplementary opening for one-half of the emitter–base junction, while the other is obstructed. The potential gradient is fixed only in the centre of the structure. Thus, because of the Hall field and of the layer resistive effect, the contact on the base is expected only in the centre of the structure. The processed structure of the bipolar lateral magnetotransistor is shown in Fig. 3.
4. Technology of fabrication The sensor is fabricated in a standard integrated circuit technology, by using an eight-mask process. Very high-quality p-type mono-crystalline silicon wafers, of resistivity ρ ≈ 7.5 cm (n0 ≈ 1015 cm−3 ) and thickness of
Fig. 2. The layout of the bipolar magnetic microsensor.
M. Avram et al. / Sensors and Actuators A 110 (2004) 259–263
261
Fig. 3. The structure of the bipolar magnetic microsensor.
approximately 350 m were used as substrate. The crystallographic orientation of wafers is (1 0 0). The first technological step involves the diffusion of a buried antimony n+ layer. This buried diffusion serves to realize the high doped region of the transistor collectors. The following high-temperature annealing (1200 ◦ C) and the subsequent high-temperature steps drive the antimony atoms 3–4 m deep into the substrate. A 12 m thick n-type epitaxial layer, 4 m thicker than the standard epitaxial layer, is grown of wafers. This epitaxial layer plus the underlying buried n+ layer will form the collector regions. The doping level of the epi-layer is approximately 6 × 1015 cm−3 . By using a proper buried n+ layer layout it is possible to create the bases. Moreover, the integrated bipolar electronics is placed in the epitaxial layer as well. To isolate different circuit elements on the chip, a p+ diffusion is carried out, the so-called p-type deep diffusion. After that, follows a phosphorus deposition and a drive-in for the n+ collector plugs. This deep n-type layer is also used for the reduction of the contact resistance to the epi-layer. After the high-temperature steps the residual oxide is stripped and a thin (1000 Å) high-quality thermal oxide is grown. Boron atoms are implanted through the oxide to form the emitter and base regions of the bipolar transistors. PECVD oxide is deposited and opened through the contact mask. A wet dip-etch is performed in order to remove completely the remaining oxide and 0.6 m thick Al/1%Si is sputtered and patterned to form the interconnects. The magnetic sensor has two buried n+ collectors separated by a small distance to eliminate the shorting effects. The epi-layer has been deposited under the collectors to enhance magnetic sensitivity. The two collectors are used as an active load of the differential preamplifier in an operational amplifier. The technological profile of the sensor can be seen in Fig. 4 that illustrates the successive technological steps (layers) for one-half of the sensor structure.
Emitter
Base Emitter Base Collector
n-Epi P+ base P+ base P N+ buried collector
P+ P substrate
Fig. 4. The technological profile of the sensor.
5. Sensor performances Fig. 5 illustrates the test set-up used for the measurements and to characterize sensor parameters.
+12V
6
+12V -12V
+5V
7
4
1
5 4
+12 2
3 1
3 + 2 +1
-12 2
B
+12
1 2 3
2
7 + -12
+ -12 3
-12V
Fig. 5. The schematic of biasing and signal conditioning circuit for the bipolar magnetotransistor.
M. Avram et al. / Sensors and Actuators A 110 (2004) 259–263
2
500
1.5
400 Offset (nA)
Magneticsensitivity (1/T)
262
1 0.5 0 0
100 200 300 400 Magnetic induction (mT)
300 200 100
500
0
Fig. 6. Magnetosensitivity variation with magnetic induction, for 2.5 mA base current.
0
0.1
0.2 0.3 0.4 Magnetic induction (T)
0.5
0.6
Magnetosensitivity (1/T)
Fig. 8. The offset variation with magnetic induction.
2.5
experimental results confirm the theoretical operating principle.
2 1.5 1 0.5
6. Conclusions
0 0
0.5
1
1.5 2 2.5 3 3.5 4 4.5 Supplied current (mA)
Fig. 7. Magnetosensitivity variation with supplied current, for a magnetic induction of 0.5 T.
All measurements are made in common base configuration. A positive voltage is applied to base from a DC voltage source VCC . The application of voltage VB between the two bases of the device causes a majority carrier current flow through the device’s active region, which leads to a certain potential distribution in the silicon substrate. The differential collector current component due to carrier deflection is a linear function of the magnetic field B, it depends on the difference of the capture area [3], and the differential collector current component due to the emitter injection modulation is an exponential function of the voltage Hall, VH : IC = IC1 − IC2 = α(IC0 , B)
VT VH /VT (e − 1)(eEH (L−1)/VT + 1) VH
(2)
To illustrate the sensor performances, we have represented the microsensor magnetosensitivity variation with the magnetic field and the supplied current in Figs. 6 and 7, respectively, and the offset current as a function of the magnetic field induction in Fig. 8. High sensitivity and low offset over large ranges of the magnetic field induction were obtained. The relative magnetosensitivity of the sensor is in the range 1–5 T−1 for measured magnetic fields less than 1 T. It increases when the supplied current in the transistor base is increased. The emitter shape, with long metal tracks, favours the offset diminution, such that the offset current is only 500 nA for measured magnetic fields up to 600 mT. The
The bipolar magnetotransistor for a surface parallel field is designed and realized in a standard integrated bipolar technology. It consists of a pair of identical vertical npn transistors anti-symmetrically oriented. Bases are made up of two diffusions with different depths. Each transistor is practically made up of two structures having different thickness and impurity concentrations within the base, and connected in parallel. High sensitivity and low offset over large ranges of the magnetic field induction are obtained.
References [1] Ch.S. Roumenin, Magnetic sensors continue to advance towards perfection, Sens. Actuators A 46–47 (1995) 273–277. [2] R. Castagnetti, M. Schneider, H. Baltes, Sens. Actuators A 46–47 (1995) 280–283. [3] R.S. Popovic, Hall Effect Devices, Adam Hilger, IOP Publishing, Bristol, England, 1991. [4] R.S. Popovic, Z. Randjelovic, D. Manic, Integrated Hall-effect magnetic sensors, Sens. Actuators A 2924 (2001) 1–5. [5] M. Avram, O. Neagoe, A new bipolar magnetotransistor with combined phenomena of carrier deflection and emitter injection modulation, in: Proceedings of the International Semiconductor Conference, Sinaia, Romania, 1996. [6] M. Avram, O. Neagoe, T. Lipan, Lateral bipolar magnetotransistors with enhanced emitter injection modulation and carrier deflection, in: Proceedings of the International Semiconductor Conference, 1997.
Biographies Marioara Avram was born in 1958 on 17th of January, in Bucharest, graduated in 1982, Faculty of Physics, University of Bucharest, and in 1990, Faculty of Automatics and Computers, “Politehnica” University of Bucharest (P.U.B.). Presently she is a senior research fellow with the National Institute for Research and Development in Microtechnologies, Bucharest, and a PhD student at the University of Bucharest. Since 1998 she is a member of the IEEE Electron Device Society. The main research interests are in the field of design and characterization of bipolar and unipolar devices, bipolar magnetotransistors, Hall sensors, and magnetic sensors based on field emission in vacuum.
M. Avram et al. / Sensors and Actuators A 110 (2004) 259–263 Cecilia Codreanu was graduated in 1972, Faculty of Electronics Engineering, “Politehnica” University of Bucharest (P.U.B.). She is currently a senior research fellow with the National Institute for Research and Development in Microtechnologies, Bucharest. The main research interests are in the field of design and characterization of BJT, JFET, MESFET transistors, and the physics of semiconductor materials: Si, GaAs, SiC. Member of the IEEE Electron Device Society.
263
Cornel Voitincu was born in 1967 on 29th of May, in Bucharest, graduated in 1992, The Electronics and Telecommunications Faculty, “Politehnica” University of Bucharest. From 1996, he is a research fellow with the National Institute for Research and Development in Microtechnologies, Bucharest. The computer assisted design (CAD) of the dipolar integrated circuits, analysis and simulation with ASIC-SPICE of electronic blocks, and schemes and interface layouts for monolitic/hibride integrated circuits are among the main research interests.