sensors Article
Fabrication Technology and Characteristics Research of a Monolithically-Integrated 2D Magnetic Field Sensor Based on Silicon Magnetic Sensitive Transistors Xiaofeng Zhao *, Chenchen Jin, Qi Deng, Meiwei Lv and Dianzhong Wen School of Electronics Engineering, Heilongjiang University, Harbin 150080, China;
[email protected] (C.J.);
[email protected] (Q.D.);
[email protected] (M.L.);
[email protected] (D.W.) * Correspondence:
[email protected]; Tel.: +86-451-8660-8457 Received: 9 June 2018; Accepted: 26 July 2018; Published: 4 August 2018
Abstract: A monolithically-integrated two-dimensional (2D) magnetic field sensor consisting of two difference structures (DSI and DSII) is proposed in this paper. The DSI and DSII are composed of four silicon magnetic sensitive transistors (SMST1, SMST2, SMST3 and SMST4) and four collector load resistors (RL1 , RL2 , RL3 and RL4 ). Based on the magnetic sensitive principle of SMST, the integrated difference structure can detect magnetic fields’ component (Bx and By ) along the x-axis and y-axis, respectively. By adopting micro-electromechanical systems (MEMS) and packaging technology, the chips were fabricated on a p-type orientation silicon wafer with high resistivity and were packaged on printed circuit boards (PCBs). At room temperature, when the V CE = 5.0 V and IB = 8.0 mA, the magnetic sensitivities (Sxx and Syy ) along the x-axis and the y-axis were 223 mV/T and 218 mV/T, respectively. The results show that the proposed sensor can not only detect the 2D magnetic field vector (B) in the xy plane, but also that Sxx and Syy exhibit good uniformity. Keywords: two-dimensional magnetic field sensor; silicon magnetic sensitive transistor; monolithic integration; difference structure; MEMS technology
1. Introduction At present, magnetic field sensors include the Hall element, giant magnetoresistance (GMR), tunneling magnetoresistance (TMR), magnetic sensitive diodes (MSD), silicon magnetic sensitive transistors (SMST), and so on [1–4]. With the development of microelectromechanical systems (MEMS) technology, magnetic field sensors have achieved a three-dimensional structure, miniaturization and integration and have a wide range of applications, such as industrial, military, aerospace and other areas [5–8]. In 2012, Chih-Ping Yu et al. proposed a two-dimensional difference folded Hall device, which integrated the lateral magnetic transistor (LMT) with the magnetoresistor (MR) [9]. When the bias current was 100 mA and the supply voltage was 2.7 V, the results show that the optimum magnetosensitivity (SRI ), optimum sensitivity (S), minimum nonlinearity error (NLE) and minimum offset were 0.385 V/(A·T), 9.564 mV/T, 4.03% and 18.85 mV, respectively. In 2013, Guo-Ming Sung et al. proposed a vertical Hall device (VHD) based on the combined magnetic effects between a bulk magnetotransistor (BMT), a vertical magnetoresistor (VMR) and a vertical magnetotransistor (VMT), which was sensitive to the magnetic induction in the plane [10]. The p-substrate was used to enhance the magnetosensitivity of BMT. The maximum supply-current-related magnetic sensitivity (SI ), maximum supply-voltage-related magnetic sensitivity (SV ) and minimum mean NLE were 1.92 V/(A·T), 42.65 mV/(V·T) and 2.11%, respectively. In 2015, Haiyun Huang et al. proposed a monolithic complementary metal oxide semiconductor (CMOS) magnetic Hall sensor with high Sensors 2018, 18, 2551; doi:10.3390/s18082551
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sensitivity and linearity characteristics [11]. The current-related sensitivity (SI ) and the voltage related sensitivity (SV ) achieved were 250 V/(A·T) at a 1-mA biasing current and 0.034 V/(V·T) at a bias voltage of 3 V. In 2017, a packaging integrated 2D magnetic field sensor was proposed, which consisted of four discrete SMSTs (the area of an SMST is 2.0 × 2.0 mm2 ) and four load resistors [12]. When the V CE = 10.0 V and IB = 6.0 mA, the magnetic sensitivities of the sensor along the x-axis and y-axis were 366.0 mV/T and 365.0 mV/T, respectively. By combining or integrating multiple magnetic sensitive devices, the 2D magnetic field (Bx and By ) in the xy plane can be measured. Based on the above references, the characteristics of sensitivity, uniformity and cross interference have been thoroughly studied. These properties have been improved by technological improvement and structural optimization. Summing up, monolithic integration has achieved greater improvement in uniformity and reduced cross interference. In this paper, a monolithically-integrated 2D magnetic field sensor was designed and fabricated by MEMS technology. In order to improve the magnetic sensitivity and uniformity, we integrated two difference structures (DSI and DSII) with four SMSTs and four collector resistors as a magnetic sensitive structure along the direction of the x-axis and y-axis, respectively. On this basis, theoretical analysis shows the effect of the magnetic field component (Bx and By ) on the output voltage of the proposed sensor. Meanwhile, the IC -V CE characteristics of SMSTs and the magnetic sensitivity of DSI and DSII were tested, and we studied the uniformity and cross interference of the magnetic sensitivity (Sxx and Syy ). 2. Basic Structure and Working Principle 2.1. Basics Structure Figure 1 shows the cubic structure of the monolithically-integrated two-dimensional (2D) magnetic field sensor, which is made up of two difference structures. The DSI consists of two SMSTs (SMST1 and SMST2) and two collector load resistors (RL1 and RL2 ) that can detect the magnetic field (Bx ) along x-axis, and two SMSTs with the opposite magnetic sensitive direction are placed symmetrically along the x-axis in xy plane. The DSII is composed of two SMSTs (SMST3 and SMST4) and two collector load resistors (RL3 and RL4 ) that exhibit the opposite magnetic sensitive direction along the y-axis. As shown in Figure 1a,b, four bases (B1 , B2 , B3 , B4 ) and four collectors (C1 , C2 , C3 , C4 ) are designed on the chip surface, and four emitters (E1 , E2 , E3 , E4 ) are designed on the back of the chip by MEMS technology. Figure 1c,d shows the cross-section of the proposed sensor along the aa0 and bb0 directions, where L is the length of the base region, w is the width of the base region and w > LD (LD is the carrier diffusion length), d is the thickness of the silicon membranes and θ is the angle between the external magnetic field vector (B) and the +x-axis of the chip surface. As illustrated in Figure 1a, the external magnetic field along the +x-axis (or +y-axis) is defined as a positive magnetic field Bx > 0 T (or By > 0 T), and the opposite direction is defined as the reverse magnetic field Bx < 0 T (or By < 0 T). 2.2. Working Principle Figure 2 presents an equivalent circuit of the proposed sensor, where the red dashed box consists of four SMSTs and four collector load resistors for the monolithically-integrated chip, in which RL1 , RL2 , RL3 and RL4 are the collector load resistors of four SMSTs, respectively. One end of RL1 , RL2 , RL3 and RL4 is connected to C1 , C2 , C3 and C4 of the SMSTs, respectively, and the other ends of RL1 , RL2 , RL3 and RL4 are connected to the supply power. Vx1 , Vx2 , Vy3 and Vy4 are the collector output voltages for SMST1, SMST2, SMST3 and SMST4, respectively. IB1 , IB2 , IB3 and IB4 are current sources that provide the base injection currents for B1 , B2 , B3 and B4 , respectively. V DD is the supply voltage. The four emitters of SMSTs are commonly grounded.
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E4 E4
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b′ b′
(d) (d) n+ Si n+ Si
p+Si p+Si
Al Al
L L
Figure 1. The basic structure of the monolithically-integrated 2D magnetic field sensor: (a) front of the Figure 1. The basic structure of the monolithically-integrated magnetic(a)field 1. The basic structure of the monolithically-integrated 2D magnetic 2D frontsensor: of the 0 ; (d)sensor: basic Figure structure; (b) back of the basic structure; (c) cross-section along aafield cross-section along bb0 . (a) front(b) ofback the of basic (b) back of the basicalong structure; cross section basic structure; the structure; basic structure; (c) cross-section aa′; (d) (c) cross-section alongalong bb′. SMST, silicon magnetic sensitive transistor. SMST, silicon sensitive transistor. aa′; (d)magnetic cross section along bb′.
V DD RL1
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By
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field sensor SMST1
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SMST3 field sensor. SMST42D magnetic Figure 2. Equivalent circuit ofSMST3 the monolithically-integrated
E 3 field sensor. E4 E3 E4 Figure 2. Equivalent circuit of the monolithically-integrated 2D magnetic (a)
SMST4
holein the xy(c)plane,electron electron As shown in Figure 3a, B is the(b) magnetic field vector where θ ishole the angle between and the +x-axis. The field components Bx and By along the x-axis andangle the y-axis As shownB in Figure 3a, B is themagnetic magnetic field vector in the xy plane, where θ is the between expressed as:The Figure 3. Working principle the monolithically-integrated 2D magnetic field sensor: B andare the +x-axis. magnetic fieldofcomponents Bx and By along the x-axis and the (a) y-axis are
expressed as:
Magnetic field vector in xy plane; (b) (c)θB≠0 T. = BT;cos ( Bx B=0 Bx = B cos θ sin θ BB y == BB sin θ y
where B is magnetic induction intensity.
(1)
(1)
where B is magnetic induction intensity. When B = 0 T, in ideal conditions, the carriers (electrons and holes) are not affected by the Lorentz When B =are 0 T,not in deflected, ideal conditions, the carriers (electrons andSMSTs holes)are areequal not affected force and so the collector currents of the four (IC1 = IC2 by = IC3the = ILorentz C4 = force and not deflected, so3b, theunder collector (IC1output = IC2 =voltages IC3 = IC4(V=x IC0 ). IC0). are As shown in Figure the currents conditionofofthe RL1four = RL2SMSTs = RL3 =are RL4equal = R0, the and Vy) of the proposed sensor are as follows:
y B3
b'
SMST3 C3 R L3
R L1
B
E4
B2 θ
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B1
RL2 a' a As shown in Figure 3b, under the zcondition y of RL1 = RL2 = RL3 = RE L43 = R0 , the output voltages (Vx and Vy ) of the proposedRL4 sensor B4 as follows: C4 are x b SMST4 ( o (a) Vx = Vx1 − Vx2 = IC2 · R L2 − IC1 · R L1(b)= 0 (2) B1 C1 C2 VB2 − V = I · R − B C 4 B4 3 3 Vy = IC3 · RCL3 =0 y3 y4 C4 L4
d
d
w
w
where IC1 , IC2 , IC3 and IC4 are the collector currents of four SMSTs, respectively.L L As shown in Figure 3c, when B 6= 0 T, under the action of Bx (Bx > 0), the carrier of SMST1 (SMST2) E E4 E2 E1 force, leading is deflected by the Lorentz to a decrease (increase)3 in the number of carriers collected SMST1 SMST2 SMST3 SMST4 by the collector region, so that IC1 decreases (IC2 increases). Similarly, under the action of By (By > 0), a′ a b IC3 and IC4 of SMST3 and SMST4 respectively. (c) are decreased and increased, (d) Vx and Vyb′are expressed as: (
Vx = Vx1 − Vx2 =SiO ( IC1 + ∆InC1+ Si )· R L1 = ∆Vx2 − ∆Vx1 SiC2 )· R Al p+Si L2 − ( IC1 2 + ∆I Vy = Vy3 − Vy4 = ( IC4 + ∆IC4 )· R L4 − ( IC3 + ∆IC3 )· R L3 = ∆Vy4 − ∆Vy3
(3)
Figure 1. The basic structure of the monolithically-integrated 2D magnetic field sensor: where ∆Vx1 , ∆Vx2 , ∆Vy3 and ∆Vy4 are the variations of the collector output voltages of SMST1, SMST2, (a) front of the basic structure; (b) back of the basic structure; (c) cross section along SMST3 and SMST4, respectively. ∆IC1 , ∆IC2 , ∆IC3 and ∆IC4 are the variations of collector currents of aa′; (d) cross section along bb′. four SMSTs, respectively. B1 C1
B1 C1
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C 2 B2
y B
By θ O
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SMST1
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x
SMST2
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hole
SMST2
E2 C4 B4
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E3
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(c)
electron
hole
SMST4
Figure 3.Figure Working principle of the monolithically-integrated 2D magnetic fieldfield sensor: (a) magnetic 3. Working principle of the monolithically-integrated 2D magnetic sensor: (a) field vector in the xy plane; (b) B = 0 T; (c) B 6 = 0 T. Magnetic field vector in xy plane; (b) B=0 T; (c) B≠0 T.
According to the definition of the magnetic sensitivities for the proposed sensor, the voltage magnetic sensitivities (Sxx and Syy ) along the x-axis and y-axis can be given: Sxx = Syy =
|Vx | Bx |Vy | By
= =
|∆Vx2 −∆Vx1 | Bx |∆Vy4 −∆Vy2 | By
= |Sx1 + Sx2 | = Sy3 + Sy4
(4)
where Sx1 , Sx2 , Sy3 and Sy4 are the voltage magnetic sensitivities of SMST1, SMST2, SMST3 and SMST4, respectively. Through theoretical analysis, magnetic field sensor with the difference structure of SMSTs can improve the magnetic sensitivity. On the basis of Equations (1)–(3), Vx and Vy can be obtained: Vx Vy
!
=
Sxx Syx
Sxy Syy
!
Bx By
! (5)
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where Sxy and Syx are the cross magnetic sensitivities of the sensors. Under ideal conditions, Sxx = Syy = S and Sxy = Syx = 0, the Sxx and Syy have a good uniformity. Then, the output voltage (V out ) can be denoted by: Vout
q
Vx 2 + Vy 2 =
q
Sxx 2 B2 cos2 θ + Syy 2 B2 sin2 θ = S·B
(6)
From Equation (5), we can see that DSI and DSII are used to achieve the measurement of the magnetic field components Bx and By in the xy plane, respectively. In addition, the V out of the proposed sensor under the action of B is calculated by Equation (6). When B is a certain value, under the ideal case, the magnetic sensitivity has good uniformity, and V out does not change with θ. After theoretical analysis, the proposed sensor has 2D magnetic sensitive characteristics and can achieve the geographic orientation measurement in plane at the same time. 3. Fabrication Technology Based on the basic structure of the proposed sensor, the chip of the sensor was fabricated on a double-sided polished p-type orientation silicon wafer with high resistivity. Figure 4 shows the main fabrication process of the sensor. The process steps are as follows: (a) cleaning the silicon wafer by using the Radio Corporation of America (RCA) standard cleaning method; (b) the first oxidation, growing the SiO2 layer by the thermal oxidation method, with a thickness of 30 nm–40 nm; (c) etching windows of the collector load resistor, injecting phosphorus ions by the ion implantation process and forming collector load resistors; (d) etching windows of the collector region, shaping the n+ regions adopted phosphorus ion implantation process, photoetching base region windows, concentrated boron injection to form p+ regions and removing the SiO2 layer of the upper surface, after re-growth of the SiO2 layer (thickness of 500 nm); (e) lithography emitter region windows, etching silicon cups by inductively-coupled plasma (ICP) and injecting phosphorus ions to form emitter junctions of four SMSTs; (f) photolithography of the lead hole; the Al layer was deposited on the surface of silicon wafer by the magnetron sputtering method, etching metal Al to form four collectors (C1 , C2 , C3 and C4 ), four bases (B1 , B2 , B3 and B4 ) and the interconnect wire on the surface of the chip, depositing the Al electrode on the back of the wafer to form a common emitter and metallization to form an ohmic contact (30 min at 420 ◦ C).
(a)
(b)
(c)
(d)
(e)
(f)
Si
SiO2
n-Si n+ Si
p+Si
Al
Figure 4. Main fabrication technology process of the proposed sensor chip: (a) cleaning the silicon wafer; Figure 4. Main fabrication technology process of the proposed sensor chip: (a) Cleaning the (b) growing thinwafer; oxide; lithography and ion implantation load resistors silicon (b)(c) Growing thin oxide; (c) Lithography andform ion implantation formand loadcollector regions; resistors andregions collector (d) Making theimplantation; base regions by and ionion implantation (d) making the base byregions; lithography and ion (e)lithography lithography and implantation; (e) Lithography and ion implantation to form four emitter regions; (f) to form four emitter regions; (f) lithography and deposition of Al electrodes and metallization to form Lithography and deposition of Al electrodes, metallization to form an ohmic contact. an ohmic contact.
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Figure 5a shows showsthe thefront front photograph of the fabricated sensor. Theof area of the chip Figure 5a photograph of the fabricated sensor. The area the chip is 2.3 mmis× Figure 5a shows the front photograph of the fabricated sensor. The area of the chip is 2.3 mm × 2.3 B1B, 4Bare , B and B are the bases, C , C , C and C are the collectors and Rthe 2.3 mm mm.× B12.3 , B2,mm. B3 and the bases, C 1 , C 2 , C 3 and C 4 are the collectors and R L1 , R L2 , R L3 and R L4 2 3 1 2 3 4 L1 , 2.3 mm. B1, B2, B3 and B4 are the bases, 4C1, C2, C3 and C4 are the collectors and RL1, RL2, RL3 and RL4 the Rcollector collector resistors of thein four SMSTs. shown in E Figure 5b,emitters E1 , E2 , Eof loadRresistors the fourload SMSTs. As shown Figure 5b, EAs 1, E 2, E3 and 4 are the L2 , RL3 and L4 are theof collector load resistors of the four SMSTs. As shown in Figure 5b, E1, E2, E3 and E4 are the emitters of3 and are the emitters of the four SMSTs, respectively. They form the common emitters. The chip was the E four SMSTs, respectively. They form the common emitters. The chip was packaged on printed 4 the four SMSTs, respectively. They form the common emitters. The chip was packaged on printed packaged on printed (PCBs) using internal lead bonding technology, is and a photograph circuit boards (PCBs)circuit usingboards internal lead bonding technology, and a photograph shown in Figure circuit boards (PCBs) using internal lead bonding technology, and a photograph is shown in Figure is5c.shown in Figure 5c. 5c.
2.3 2.3mm mm
B 3 CC3 3RRL3 L3 R L1B 3 RL1 BB2 2 C 1 C1 CC2 2 B 1 B1 RRL2L2 RRL4L4 CC4 4 BB4 4 2.3mm mm 2.3 (a) (a)
SMST3 SMST3
EE3 3 EE2 2
EE1 1 EE4 4 (b) (b)
SMST1 SMST1
SMST2 SMST2
SMST4 SMST4 (c) (c)
Figure 2D2D magnetic field sensor: (a) (a) front of Figure5.5.Photograph Photographofofthe thechip chipofofthe themonolithically-integrated monolithically-integrated magnetic field sensor: front Figure 5. Photograph of the chip of the monolithically-integrated 2D magnetic field sensor: (a) front the chip; (b)(b) back of the chip; (c)(c) photograph of of thethe packaging of of the monolithically-integrated chip. of the chip; back of the chip; photograph packaging the monolithically-integrated chip. of the chip; (b) back of the chip; (c) photograph of the packaging of the monolithically-integrated chip.
4. Characteristics Characteristics of ofthe the2D 2DMagnetic MagneticField FieldSensor Sensor 4. 4. Characteristics of the 2D Magnetic Field Sensor 4.1. 4.1. Testing TestingSystem System 4.1. Testing System Figure Figure 66 shows shows the the testing testing system system of of the the proposed proposed sensor, sensor, which which consists consists of of aa magnetic magnetic field field Figure 6 shows the testing system of the proposed sensor, which consists of a magnetic field generator generator(CH-100, (CH-100,Cuihai, Cuihai, Beijing, Beijing, China), China), aa multi-meter multi-meter (Agilent (Agilent 34401A, 34401A, Agilent, Agilent, Santa Santa Clara, Clara, CA, CA, generator (CH-100, Cuihai, Beijing, China), a multi-meter (Agilent 34401A, Agilent, Santa Clara, CA, USA), a programmable linear DC power source (DP832A, RIGOL, Beijng, China) and a rotating USA), a programmable linear DC power source (DP832A, RIGOL, Beijng, China) and a rotating USA), a programmable linear DC power source (DP832A, RIGOL, Beijng, China) and a rotating platform. At room room temperature, temperature, we we studied characteristics of of the the SMSTs platform. At studied the the IIC-V -VCE characteristics SMSTs using using aa platform. At room temperature, we studied the ICC-VCECEcharacteristics of the SMSTs using a semiconductor semiconductor characteristic characteristic analysis analysis system system (KEITHLEY (KEITHLEY 4200, 4200, Keithley, Keithley, Cleveland, Cleveland, OH, OH, USA). USA).On On semiconductor characteristic analysis system (KEITHLEY 4200, Keithley, Cleveland, OH, USA). On this this basis, basis, the the magnetic magnetic sensitive sensitive characteristics characteristics for for the the 2D 2D magnetic magnetic field field sensor sensor were were tested tested using using this basis, the magnetic sensitive characteristics for the 2D magnetic field sensor were tested using the the testing testing system. system. In In the the testing testing process, process, the the chip chip of of sensor sensor was was placed placed on on the the surface surface of of aarotating rotating the testing system. In the testing process, the chip of sensor was placed on the surface of a rotating platform. platform. By By adopting adopting aa rotating rotating platform platform with with aa programmable programmable motor, motor, we we adjusted adjusted the the angle angle (θ) (θ) platform. By adopting a rotating platform with a programmable motor, we adjusted the angle (θ) between between the the constant constant magnetic magnetic field field vector vector (B) (B) and and the the magnetic magnetic sensitive sensitive direction direction for for the the x-axis x-axis between the constant magnetic field vector (B) and the magnetic sensitive direction for the x-axis sensor. Equations (1)–(3), when B is B constant, the relationship curves curves between the output sensor.According Accordingtoto Equations (1)–(3), when is constant, the relationship between the sensor. According to Equations (1)–(3), when B is constant, the relationship curves between the voltage (V and V ) and the θ are tested. output voltage (Vx and Vy) and the θ are tested. x output voltage (Vx yand Vy) and the θ are tested.
Figure 6. 6. The The test test system system of of the the monolithically-integrated monolithically-integrated2D 2Dmagnetic magneticfield fieldsensor. sensor. Figure Figure 6. The test system of the monolithically-integrated 2D magnetic field sensor.
4.2. IC-VCE Characteristics of the SMSTs 4.2. IC-VCE Characteristics of the SMSTs In a range of supply collector voltage of 0 V–6.0 V (the test step is 0.2 V) and a base injection In a range of supply collector voltage of 0 V–6.0 V (the test step is 0.2 V) and a base injection current (IB) of 8.0 mA, the effect of the external magnetic field (B = 0 T, B = ±0.3 T and B = ±0.6 T) on current (IB) of 8.0 mA, the effect of the external magnetic field (B = 0 T, B = ±0.3 T and B = ±0.6 T) on
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4.2. IC -VCE Characteristics of the SMSTs
0.60
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0.00 6.0
Bx=-0.6T Bx=-0.3T Bx= 0.0T 0.20 Bx= 0.3T Bx= 0.6T 0.00 4.0 6.0
Bx=-0.6T Bx=-0.3T Bx=0.0T Bx=0.3T Bx=0.6T 4.0
2.0
0.0
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IC1 (mA)
In a range of supply collector voltage of 0 V–6.0 V (the test step is 0.2 V) and a base injection Sensors 2018, 18, x FOR PEER REVIEW 7 of 11 current (IB ) of 8.0 mA, the effect of the external magnetic field (B = 0 T, B = ±0.3 T and B = ±0.6 T) on of SMSTs was researched. a magnetic field is applied thealong chip CE characteristics thethe IC-VICCE-V characteristics of SMSTs was researched. WhenWhen a magnetic field is applied on theon chip along the x-axis direction, Figure 7a,b shows the I -V characteristic curves of SMST1 and SMST2 C CE the x-axis direction, Figure 7a,b shows the IC-VCE characteristic curves of SMST1 and SMST2 at at different T). We We can different BBxx (and (and B Byy == 00 T). can see see that that SMST1 SMST1 and and SMST2 SMST2 have have the the opposite opposite magnetic magnetic sensitive sensitive characteristics. > 1.8 V, the IC1ofofSMST1 SMST1keeps keepsincreasing increasing in in the the whole whole magnetic magnetic field field range characteristics. When WhenV VCE CE > 1.8 V, the IC1 range from the positive magnetic field to the negative magnetic field. However, in the same condition, the Ithe C2 from the positive magnetic field to the negative magnetic field. However, in the same condition, of keeps decreasing. It was alsoalso shown thatthat when V CEVwas a fixed value and Bx >B0x >T,0the IC1 IC2SMST2 of SMST2 keeps decreasing. It was shown when CE was a fixed value and T, the of decreased with Bx and thethe IC2IC2 ofof SMST2 increased with BxB. xWhen SMST1 IC1SMST1 of SMST1 decreased with Bx and SMST2 increased with . WhenBxBx 0 T (or Bx < 0 T), ∆IC1 is less than zero (or greater than zero) and ∆IC2 value is is greater than zero (or less than zero). When Bx is a fixed value, the absolute value of ∆IC1 and ∆IC2 greater than zero (or less than zero). When Bx is a fixed value, the absolute value of ∆IC1 and ∆IC2 increases with IB . As shown in Figure 8b, under the same conditions, ∆IC3 and ∆IC4 are similar to increases with IB. As shown in Figure 8b, under the same conditions, ∆IC3 and ∆IC4 are similar to those of ∆IC1 and ∆IC2, respectively. The experimental results showed that VCE and Bx (By) were fixed values, the absolute value of ∆IC1, ∆IC2, ∆IC3 and ∆IC4 linearly increasing with IB. In light of Figure 2, the input-output characteristics of the SMSTs tested under VCE = 5.0 V and IB = 8.0 mA are shown in Figure 9. When B = Bx, it can be seen from Figure 9a that when B > 0 T (or B < 0 T), Vx1 increases with B and Vx2 decreases with B (or Vx1 decreases with B and Vx2 increases with B). The experimental results showed that SMST1 and SMST2 had the opposite magnetic field sensitive
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those of ∆IC1 and ∆IC2 , respectively. The experimental results showed that V CE and Bx (By ) were fixed values, the absolute value of ∆IC1 , ∆IC2 , ∆IC3 and ∆IC4 linearly increasing with IB . In light of Figure 2, the input-output characteristics of the SMSTs tested under V CE = 5.0 V and IB = 8.0 mA are shown in Figure 9. When B = Bx , it can be seen from Figure 9a that when B > 0 T (or B < 0 T), Vx1 xincreases with B and Vx2 decreases with B (or Vx1 decreases with B and Vx2 increases Sensors 2018, 18, FOR PEER REVIEW 8 of 11 with B). The experimental results showed that SMST1 and SMST2 had the opposite magnetic field Sensors 2018, 18, x FOR PEER REVIEW 8 of 11 sensitive directions, while V and V were almost unchanged, indicating that the magnetic field y3 y4 unchanged, indicating that the magnetic field applied in the directions, while Vy3 and Vy4 were almost applied inofthe ofVthe x-axis had little effect on SMST3that andthe SMST4. directions, while Vy3 and y4 were almost magnetic field applied in the direction thedirection x-axis had little effect onunchanged, SMST3 andindicating SMST4. direction of the x-axis had little effect on SMST3 and SMST4. Ib=6mA
IbI=8mA =6mA
IIb=8mA =6mA
IbI=10mA =8mA
IIb=10mA =8mA
Ib=10mA
Ib=10mA
b
-0.03
b
△ I (mA) △ IC1 C1 (mA)
-0.03 -0.03
0.03
0.00
C2
0.03
0.0 0.0 BBxx (T) (T)
Ib=10mA
Ib=10mA
b
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b
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Ib=8mA Ib=6mA Ib=10mA I =8mA
△ IC4 (mA)
0.00
0.03 0.03
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Ib=6mA
Ib=8mA Ib=6mA Ib=10mA I =8mA
-0.3
0.0
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0.0 y (T) By B(T)
(a) (a)
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0.00 0.00
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0.06
b
b
-0.06 -0.06 -0.6 -0.6
0.06
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△△IC2I (mA) (mA)
0.03 0.03
-0.06
Ib=6mA
△ IC3 (mA) △ IC3 (mA)
0.06 0.06
0.06
0.06 0.6 0.6
(b)(b)
Figure 8.8.Relationship Relationship curves ∆I andBBBofof of the four SMSTs: (a) SMST1 and SMST2; (b) SMST3 SMST3 Figure between∆I ∆ICCCand and the four SMSTs: SMST1 and SMST2; Figure8. Relationship curves curves between between the four SMSTs: (a)(a) SMST1 and SMST2; (b) (b) SMST3 and SMST4. and andSMST4. SMST4.
2.76 2.76
2.76 2.76 VVx1
VVx2 x2
Vy3 V
x1
Vy4 V y4
V (V) Voutout(V)
Vout (V) Vout (V)
y3
VVy3
2.68 2.68
y3
Vx1 V x1
2.68 2.68
Vy4
Vx2
Vy4
2.60 2.60-0.6 -0.6
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-0.3
0.0 B0.0 (T)
B (T) (a)
(a)
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2.60 2.60 -0.6
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-0.3
-0.3
0.0 B (T)0.0
0.3
0.3
Vx2
0.6
0.6
B (T)
(b)
(b)
Figure9.9.Relationship Relationshipcurves curves between between V SMSTs: (a)(a) B =BB=x; B(b) B =B By= . By . Figure Vout andBBofofthe the SMSTs: outand x ; (b)
Figure 9. Relationship curves between Vout and B of the SMSTs: (a) B = Bx; (b) B = By.
Moreover, under the same conditions, when the magnetic field was applied along the y-axis Moreover, under same conditions, when the the magnetic magnetic field field was was applied applied along the the y-axis Moreover, under the the samevoltage conditions, when y-axis direction, the collector output of SMST3 and SMST4 were similar to those ofalong SMST1 and direction, the collector output voltage of SMST3 and SMST4 were similar to those of SMST1 and direction, the collector output voltage of SMST3 and SMST4 were similar to those of SMST1 SMST2, respectively. As a result, Figure 9b reveals that when the magnetic field was applied alongand SMST2, respectively. As a result, Figure 9b reveals that when the magnetic field was applied along SMST2, respectively. As a result, 9b reveals that the magnetic field wasIn applied along the y-axis, it only affected SMST3 Figure and SMST4 and had thewhen opposite sensitive direction. line with the y-axis, it only affected SMST3 and SMST4 and had the opposite sensitive direction. In line with the y-axis, it(4), only andsensitivities SMST4 and(Shad the opposite direction. linebe with Equation theaffected voltage SMST3 magnetic x1, Sx2 , Sy3 and Sy4sensitive ) of the four SMSTsIncan Equation (4), the voltage magnetic sensitivities (S , S , S and S ) of the four SMSTs can be y4 Equation thethevoltage magnetic sensitivities x1, V Sx2 x2and , Sy3y3 y4 ) of four SMSTs calculated(4), from experimental results. When VCE (S = x1 5.0 IB and = 8.0 S mA, Sx1,the Sx2, S y3 and Sy4 are can 115 be calculated the experimental results. V 5.0VVand andIBIB= =8.0 8.0mA, mA,Sx1S,x1S,x2S, x2 Sy4 115 are y3 and CE==5.0 mV/T, 108from mV/T, mV/T and 112 mV/T,When respectively. calculated from the106 experimental results. When VCE Sy3, Sand Sy4 are 115 mV/T, 108 mV/T, 106 mV/T and 112 mV/T, respectively. curvesand between Vx (Vrespectively. y) of the x-axis and y-axis sensors and B are shown in mV/T,The 108 relationship mV/T, 106 mV/T 112 mV/T, The10, relationship curves V (Vyy))of oflinearity the x-axis x-axis and y-axisB, sensors and are sensor shown in in Figure which shows that Vbetween x and Vy had better withand changing and theand proposed The relationship curves between Vxx (V the y-axis sensors BB are shown Figure which that and As Vyyhad hadbetter better linearity with(4), changing and theand proposed sensor could 10, detect the shows 2D magnetic obtained from Equation Sxx and B, SB,yyand of DSІ DSII were Figure 10, which shows that V Vxxfield. and V linearity with changing the proposed sensor could detect the 2D magnetic field. As obtained from Equation S S of DSI and DSII were 223 mV/T and 218 mV/T, respectively. Based on Equation (5), S xy(4), and S yxand of DSІ and DSII were 0.43 xx yy could detect the 2D magnetic field. As obtained from Equation (4), Sxx and Syy of DSІ and DSII were mV/T and 0.08 mV/T, respectively. On the basis of the definition of cross interference [13], the cross 223 mV/T and 218 mV/T, respectively. Based on Equation (5), S and S of DSI and DSII were xy Syx ofyxDSІ and DSII were 0.43 223 mV/T and 218 mV/T, respectively. Based on Equation (5), Sxy and interference was found to be 0.19% and 0.04%, respectively. The results showed that the sensitivities 0.43 mV/T and 0.08 mV/T, respectively. On the basis of the definition of cross interference [13], mV/T and 0.08 mV/T, respectively. On the basis of the definition of cross interference [13], the cross of the sensor could be improved with better uniformity and lower cross interference.
interference was found to be 0.19% and 0.04%, respectively. The results showed that the sensitivities of the sensor could be improved with better uniformity and lower cross interference.
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the cross interference was found to be 0.19% and 0.04%, respectively. The results showed that the sensitivities the sensor could be improved with better uniformity and lower cross interference. Sensors 2018, 18,ofx FOR PEER REVIEW 9 of 11 0.20 Vx
0.00
-0.10
Vx (V)
0.00
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(a)0.0
0.3
V
x
0.20
Vy
0.10
0.10 Vy (V)
0.10 Vy (V)
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Vy
Vx (V)
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-0.20 (b)
-0.6
-0.3
B (T)
0.0 B (T)
(a)
(b)
(c)
0.3
-0.20 0.6
Figure10. 10.Relationship Relationshipcurves curvesofofVVx ~B, x~B,V Vyy~B ~B of sensor: (a) Figure of the the 2D 2D magnetic magnetic field field sensor: (a) B B == BBxx;;(b) (b)BB==BBy.y .
4.4. Characteristics 2D Magnetic Magnetic Field Field Sensor Sensor 4.4. Characteristics of of the the 2D When V VDD = 5.0 V and shows the relationship relationship curves curves between between VVxx (V (Vyy)) When and IIBB ==8.0 8.0mA, mA, Figure Figure 11a,b 11a,b (e) shows the DD = 5.0 V(d) (f) ◦ ◦ ◦ and rotation rotation angle angle θθ (from (from 00°to to 360 360° with with aa step step of of 55°). Under the the condition condition of B= = 0.4 we rotated rotated and ). Under of B 0.4 T, T, we ◦ the chip, when θ = 0° (B = B x and By = 0 T), Vx was maximum and Vy was approximately zero. With the chip, when θ = 0 (B = Bx and By = 0 T), Vx was maximum and Vy was approximately √ zero. ◦theory, n-Si When n+=Si45°, p+Si Al B =BxB==By 2B 2 the increasing of θ, of Vy θ,increased and V xSidecreased. When θ , the 22B/2, With the increasing Vy increased and Vx SiO decreased. θ = in 45 , in theory, = x y ◦ the experimental results showed that = 53.1 mV and = 58.9 mV.When Whenθθ == 90°, 90 , the the experimental experimental experimental results showed that Vx V=x53.1 mV and VyV=y 58.9 mV. results showed that V = − 6.5 mV and V = 80.1 mV. From Figure 11a, we can see that and Vy x y x the Figure 4. Main fabrication technology of the proposed sensor (a) Cleaning results showed that Vx = −6.5 mV and Vy = 80.1 process mV. From Figure 11a, we canchip: see that Vx andVV y varied varied with θ and conformed to the sine and cosine functional relationship. Through the analysis wafer; to (b)the Growing thincosine oxide;functional (c) Lithography and ionThrough implantation form loadof the with θ andsilicon conformed sine and relationship. the analysis of the experimental results, the proposed sensor could detect Bxregions and in the plane,and respectively. resistors and collector regions; (d) could Making the base lithography ion y by experimental results, the proposed sensor detect Bx and By Bin the xyxyplane, respectively. According to Equation (6), we calculated the V of the sensor at different rotation angles. Figure implantation; (e) Lithography and ion implantation to form four emitter regions; (f) 11b out According to Equation (6), we calculated the Vout of the sensor at different rotation angles. Figure 11b shows the relationship curves between V and θ, and V was close to the circular. The results Lithography and deposition of Al electrodes, metallization to form an ohmic contact. shows the relationship curves between Vout out and θ, and Vout out was close to the circular. The results showed along the the x-axis showed that that the the magnetic magnetic sensitivities sensitivities along x-axis and and y-axis y-axis direction direction of of the the 2D 2D magnetic magnetic field field sensor approached uniformity. sensor approached uniformity. 00
120 120
(a)
60 60
00
-50 -50
180 180 。 。 (( ))
(a) (a)
270 270
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300 300
6060
00270 270
60 60
90 90
3030
Vout (mV) Vout (mV)
Vyy
50 50
-100 -100 00
330 330
Vxx
Vout (mV) (mV) V out
VVxx,, V Vyy (mV) (mV)
100 100
120 120
9090
240 240
120 120 210 210
180 180
150 150
(b) (b)
Figure 11. Relationship curves between the output voltage and rotation angle θ of the proposed Figure 11. Relationship curves between the output voltage and rotation angle θ of the proposed sensor: 11.and Relationship sensor:Figure (a) Vx~θ Vy~θ; (b) Vcurves out~θ. between output voltage and rotation angle θ of the proposed (a) Vx ~θ and Vy ~θ; (b) V out ~θ. sensor: (a) Vx~θ and Vy~θ; (b) Vout~θ.
Table 1 gives a summary of the performance of the 2D magnetic field sensors [9–12]. In this work, Table 1 gives a summarymagnetic of the performance the 2D fieldand sensors In load this the monolithically-integrated field sensorofbased onmagnetic four SMSTs four [9–12]. collector work, the monolithically-integrated magnetic field sensor based on four SMSTs and four collector load resistors had higher magnetic sensitivity and lower cross interference. resistors had higher magnetic sensitivity and lower cross interference.
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Table 1. Performance summary and comparison of 2D magnetic field sensors. Reference Parameters
Magnetic Sensitive Structure
Supply Voltage
Magnetic Sensitivity
Cross Interference
Chip Area
[9]
Hall device
2.7 V
9.56 mV/T
0.259 mV (B = 150 mT) 0.330 mV (B = 150 mT)
2.0 × 1.0 mm2
[10]
Vertical Hall device
—
Sx = 40.06 mV/(V·T) Sy = 42.65 mV/(V·T)
12.55 mV/(V·T) 12.33 mV/(V·T)
—
[11]
Hall device
5.0 V
34.0 mV/(V·T)
—
60.0 × 60.0 µm2
[12]
Magnetic sensitive transistor
V CE = 10.0 V IB = 6.0 mA
Sx = 366 mV/T Sy = 365 mV/T
—
7.0 × 7.0 mm2
This work
Magnetic sensitive transistor
V CE = 5.0 V IB = 8.0 mA
Sx = 223 mV/T Sy = 218 mV/T
0.19% 0.04%
2.3 × 2.3 mm2
5. Conclusions In summary, a monolithically-integrated 2D magnetic field sensor was designed and fabricated on a silicon wafer with the direction (ρ > 100 Ω·cm) using MEMS technology and packaged on PCBs. It consisted of two difference structures with four SMSTs and four collector load resistors. When V CE = 5.0 V and IB = 8.0 mA, the magnetic sensitivities of the two difference structures for the proposed sensor were 223 mV/T and 218 mV/T, respectively. The Sxx and Syy were approximately equal, indicating that the magnetic sensitivity of the proposed sensor had better uniformity. Through the characteristics analysis of the proposed sensor, the relationship curves between output voltage (Vx , Vy ) and θ conformed to the sine function and cosine function at a constant external magnetic field (B), so the proposed sensor could detect the magnetic field vector B in the xy plane and exhibited lower cross interference, which lays the foundation for the research on the measurement of a 2D magnetic field and for the monolithic integration of the sensor. Author Contributions: Supervision, X.Z. and D.W.; Validation, C.J., M.L.; Visualization, Q.D.; Writing, original draft, X.Z., C.J. and Q.D.; Writing, review and editing, X.Z. Funding: Project supported by the National Natural Science Foundation of China (Grant Nos. 61471159, 61006057), the Special Funds for Science and Technology Innovation Talents of Harbin in China under Grant 2016RAXXJ016 and the Modern Sensor Technology Innovation Team for the College of Heilongjiang Province in China (Grant No. 2012TD007). Conflicts of Interest: The authors declare no conflict of interest.
References 1. 2.
3. 4.
5. 6.
Roumenin, C.S.; Nikolov, D.; Ivanov, A. A novel parallel-field Hall sensor with low offset and temperature drift based 2D integrated magnetometer. Sens. Actuators A Phys. 2004, 115, 303–307. [CrossRef] Herrera-May, A.L.; Soler-Balcazar, J.C.; Vázquez-Leal, H.; Martínez-Castillo, J.; Vigueras-Zuñiga, M.O.; Aguilera-Cortés, L.A. Recent advances of MEMS resonators for lorentz force based magnetic field sensors: Design, Applications and Challenges. Sensors 2016, 16, 1359. [CrossRef] [PubMed] Zhao, X.F.; Li, B.Z.; Wen, D.Z. Fabrication technology and characteristics of a magnetic sensitive transistor with nc-Si:H/c-Si heterojunction. Sensors 2017, 17, 212. [CrossRef] [PubMed] Sander, C.; Leube, C.; Paul, O. Novel compact two-dimensional CMOS vertical Hall sensor. In Proceedings of the 2015 Transducers—2015 18th International Conference on Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS), Anchorage, AK, USA, 21–25 June 2015; pp. 1164–1167. Roumenin, C.S. Magnetic sensors continue to advance towards perfection. Sens. Actuators A Phys. 1995, 46-47, 273–279. [CrossRef] DJiles, C.; Lo, C.C.H. The role of new materials in the development of magnetic sensors and actuators. Sens. Actuators A Phys. 2003, 106, 3–7.
Sensors 2018, 18, 2551
7.
8. 9. 10. 11. 12. 13.
11 of 11
Banjevic, M.; Furrer, B.; Popovic, R.S. 2D CMOS integrated magnetometer based on the miniaturized circular vertical Hall device. In Proceedings of the 2009 International Solid-State Sensors, Actuators and Microsystems Conference, Denver, CO, USA, 21–25 June 2009; pp. 877–880. Zhao, X.F.; Wen, D.Z.; Zhuang, C.C.; Cao, J.; Wang, Z. Fabrication and characteristics of the magnetic field sensors based on nano-polysilicon thin-film transistors. J. Semicond. 2013, 34, 036001. [CrossRef] Yu, C.P.; Sung, G.M. Two-dimensional folded CMOS Hall device with interacting lateral magnetotransistor and magnetoresistor. Sens. Actuators A Phys. 2012, 182, 6–15. [CrossRef] Sung, G.M.; Yu, C.P. 2-D differential folded vertical Hall device fabricated on a P-Type substrate using CMOS technology. IEEE Sens. J. 2013, 13, 2253–2262. [CrossRef] Huang, H.Y.; Wang, D.J.; Xu, Y. A monolithic CMOS magnetic Hall sensor with high sensitivity and linearity characteristics. Sensors 2015, 15, 27359–27373. [CrossRef] [PubMed] Yang, X.H.; Zhao, X.F.; Bai, Y.J.; Wen, D. Two-Dimensional magnetic field sensor based on silicon magnetic sensitive transistors with differential structure. Micromachines 2017, 8, 95. [CrossRef] Lozanova, S.; Noykov, S.; Roumenin, C. Three-dimensional magnetometer based on subsequent measurement principle. Sens. Actuators A Phys. 2015, 222, 329–334. [CrossRef] © 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
