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New ISFET sensor interface circuit for biomedical applications
Sensors and Actuators B 57 (1999) 63 – 68
New ISFET sensor interface circuit for biomedical applications B. Pala´n b,*, F.V. Santos a, J.M. Karam a, B. Courtois a, M. Husa´k b b
a TIMA Laboratory, 46 a6enue Fe´lix Viallet, Grenoble, France Department of Microelectronics, Czech Technical Uni6ersity in Prague, Faculty of Electrical Engineering, Technicka´ 2, 166 27 Prague 6, Czech Republic
Received 16 October 1998; received in revised form 29 January 1999; accepted 8 February 1999
Abstract This article presents a novel architecture of an ISFET sensor interface circuit, monolithically integrated on a 3D MCM, part of a biomedical microsystem. It is a differential configuration with two ISFET devices (one with Si3N4 ion sensitive layer, the other with SiO2 sensitive layer) and realized in a 2.5 mm CMOS technology. The sensor interface is simple, has a current output signal and low silicon area requirements. The circuit architecture provides digital facilities, which makes possible the performance of the configuration been optimized during a calibration step of the system. © 1999 Elsevier Science S.A. All rights reserved. Keywords: ISFET sensor; Analog ASIC design; ISFET sensor interface
1. Introduction The desirable property of a microsystem for medical applications is to realize chemically sensitive sensors with conventional IC technologies that have very small dimensions and fast response. This article presents a novel architecture of an ISFET sensor interface circuit which has been integrated as a part of a sensor module of a biomedical microsystem. This chip contains also several other sensors, for measuring temperature and pressure of the incoming liquid [1], in addition to the ISFET-based pH sensors. Two ISFET devices and the differential analog interface are monolithically integrated, using a 2.5 mm CMOS technology from CNM, Barcelona, Spain [2]. The interface is optimized for use in the medical microsystem which implies the restrictions to the CMOS process and a low power consumption. As sensors often have unpredictable specifications, a high degree of flexibility is also required for the sensor interface. In that way, the characteristics can be adapted to the actual specifications of the sensor. The analog interface circuit proposed for the sensors is equipped with digital con* Corresponding author. Tel.: + 33-4-76574770; 76473814. E-mail address: [email protected] (B. Pala´n)
fax:
+33-4-
trol facilities for both addressing and adapting their characteristics. A voltage-to-current (V–I) converter generates a current output because of its perfectly integration to the A/D converter (current input oversampling sigma–delta) selected for the microsystem. 2. ISFET sensors The principle of measuring the concentration of chemical quantities with a solid-state device, called ISFET, was introduced in 1970 by P. Bergveld [3]. The first reported ISFETs were devices with a SiO2 gate insulating layer [4]. Because of its hydrating and highly unstable properties, the possibility of using other ionsensitive materials (Si3N4, Al2O3, Ta2O5) was very soon an object of research. Each layer has some important properties, influencing the ISFET’s performance. These properties are sensitivity, selectivity, long-term drift, response time and temperature dependency. A good summary of chemical response of various fabricated pH ISFETs was given in Matsuo and Esashi [5]. When ISFET and CMOS compatibility is desired, silicon nitride is the best choice as a sensitive membrane due to its sensitivity, long term stability and high resistance to hydration. Si3N4 is also a well known material in microelectronics and it is extensively used in CMOS technology.
0925-4005/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved. PII: S 0 9 2 5 - 4 0 0 5 ( 9 9 ) 0 0 1 3 6 - 7
B. Pala´n et al. / Sensors and Actuators B 57 (1999) 63–68
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Fig. 1. (a) CNM ISFET sensor layout, and (b) the ISFET model including drain and source series resistances.
Fabrication of ISFET of different sensitivities is necessary for the proper operation of a differential configuration. Both our sensors are active and monolithically integrated together with the sensor interface. One ISFET is covered by a Si3N4 sensitive layer, the second one is covered only with a SiO2 layer. The second ISFET is much poorer [5], with significant non-linearity, but it can be used to demonstrate the circuit function and technology compatibility. A physical layout of one ISFET is shown in Fig. 1a. The dimensions of the sensor gate are 400/20 mm. The L must be at least 20 mm, to insure a good contact with the liquid at the gate, and W must be at least 400 mm for an acceptable transistor b. The reference electrode (Pt type) is not shown in the layout. Fig. 1b illustrates an ISFET electrical model including source and drain series resistances. In the configuration of the ISFET sensor, the electrical contacts to the drain and source are not close to the actual transistor drain and source terminals. In practice, the area surrounding the gate is completely covered with protecting and insulating layers and in the vicinity of this region, no metal contacts can exist, so the contact places are usually some millimeters away. In this case, the ISFET internal drain and source resistances for the structure in Fig. 1a are
Table 1 Properties of used ISFET sensors Device
ISFET1
ISFET2
Sensitive layer Sensitivity DVth Size of sensor’s gate W/L Vt0 (zero-bias)
Si3N4 52–58 mV/pH 400/20 mm −2.9 V
SiO2 24–36 mV/pH 330/20 mm −2.9 V
about 100 V. Because these series resistances seriously influence the ISFET’s electrical behaviour, they should be taken into account in the ISFET model. Moreover, a parasitic capacitances drain-substrate, source-substrate of several tens of pF have to be added to the ISFET simulation model. Table 1 summarizes properties of both used sensors.
3. Sensor interface design In general, single ISFET interface circuits do not offer any degree of compensation for temperature dependency or long-term drift. Therefore, several ISFET differential configurations have been studied. The difference is taken at the output signals of two ISFETs implemented in the same solution and using the same reference electrode. Temperature dependency as well as common noise compensation can be reduced to a certain level. Instability caused by the membrane layers of the ISFETs and the unstable electrolyte-reference electrode potential problem will be also solved. The global sensor interface configuration is presented in Fig. 2. It consists of two source-and-drain follower circuits and a voltage-to-current converter. The reference electrode is grounded since a sample liquid can be conductive and metallic parts of the microsystem will be probably grounded also. Two identical read-out circuits are used for each ISFET sensor, as shown in Fig. 2 (see subcircuit in a dashed line). The drain current of the ISFET1 (ISFET2) is driven by the current sink Is2 (Is22) and the drain-source voltage Vds is fixed by the current source Is1 (Is11) and resistor RsetA (RsetB) [6]. A change in ion activity will lead to a change of the common mode level of Vds with respect to ground. Both ISFETs work in the
B. Pala´n et al. / Sensors and Actuators B 57 (1999) 63–68
65
Fig. 2. Differential ISFET sensor interface scheme.
Fig. 3. Simulation plot of two ISFET source-and-drain followers, pH sweep, at room temperature.
linear region. When Vg =0V and Vgs = −Vs = −VoutA, the expression for VoutA is derived as: VoutA = − Vth −
Is2 I ·R − s1 setA b·Is1·RsetA 2
(1)
When b, RsetA, Is1 and Is2 are constants, VoutA is proportional to a change in ion activity ai represented by the threshold voltage Vth of the ISFET1 sensor. VoutB signal can be obtained similarly. Identical current sources Is1 and Is11 have been designed using the cascode current source architecture with 20 mA currents [7]. Low voltage cascode current sinks Is2, Is22 have been designed to have also the same quiescent currents of 55 mA. Both RsetA, RsetB from Fig. 2 are made as P+ diffusions in N-wells to form 10 kV resistors. The
same approach is applied with the design of four voltage followers A1, A11 (A2, A22). All followers have been realized with PMOS input transistors with the maximum offset of 2 mV, and able to drive 200 pF capacitive load (ISFET’s drain and source parasitic capacitances). Linear V–I converter with differential PMOS inputs has been designed based on the first-order square-law characteristics of MOS transistors biased in saturation [8] to have the transconductance constant Iout/Vin = 5 mA/0.1 V. Voltage supplies for all the interface were applied to Vdd = 5 V and VdH = 6 V (for V–I converter). Simulation plot of two ISFET source-and-drain voltage follower circuits presents Fig. 3. The total current output response of the differential ISFET interface represents Fig. 4.
B. Pala´n et al. / Sensors and Actuators B 57 (1999) 63–68
66
Simulated results showed that this analog interface would be able to measure pH concentration with the precision of 9 0.15 pH. A microphotograph of the fabricated sensor circuit is shown in Fig. 5.
4. Results and discussion An extended set of electrical and pH tests have been carried out in order to prove the proper circuit functionality. Firstly, electrical characterization programme has been prepared. The input offset of maximum 2 mV has been measured within the input voltage range from 0.4 to 2.8 V of all voltage followers. Low voltage cascode current sinks work from 0.4 V. The cascode current sources operate up to 3 V. The linear V–I converter has the tranconductance constant about Iout/ Vin =5 mA/0.1 V as it has been designed. The measured signal at the output of the V – I converter compared with the simulation plot presents Fig. 6.
Secondly, five buffer solutions have been applied for pH tests (pH 4.01; 6.86; 7.00; 9.18; and 10.01). An external Fe microprobe needle has been used as a reference electrode (technology difficulties of Pt electrode integration on the chip). The measurements were done in the dark and with permanent stirring of the liquid. Unfortunately, the ISFET2 sensor has been found inactive with the grounded reference electrode due to a technological error [9] (its zero-bias threshold voltage has been set to Vto = + 0.6 V than was required in Table 1), and thus the VoutB signal approached zero. Only VoutA signal has been successfully recorded and shown in Fig. 7. The measured signal can be compared with its simulation from Fig. 3. It is shifted up about + 0.7 V because of the other reference electrode potential. Even though the differential configuration has not been fully tested during the pH measurements, the feasibility and functionality of the ISFET sensor circuit has been verified.
Fig. 4. Total simulation plot of the ISFET sensor interface at room temperature, pH sweep.
Fig. 5. Die microphotograph of the all monolithic differential ISFET sensor interface.
B. Pala´n et al. / Sensors and Actuators B 57 (1999) 63–68
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Fig. 6. Measured result at the current output.
Fig. 7. VoutA output signal as function of the pH concentration at room temperature.
5. Conclusions
References
This paper described design and tests of the novel ISFET sensor interface, a part of a biomedical microsystem. The CMOS differential configuration with two ISFETs includes two source-and-drain follower circuits and the V– I converter. Temperature dependency of the ISFETs can be minimized by choosing an optimal value for the current sinks and sources during a calibration step of the system. Differential configuration is adaptable for each ISFET device. It can become a suitable sensor interface for biomedical applications.
[1] R. Wissing, J.M. Karam, Design of the Integrated Electronics for the BARMINT Medical Demonstrator, TIMA technical report, Grenoble, France, 1995. [2] Design Rules and SPICE Parameters for the CMOS CNM25 Technology, CNM, Barcelona, Spain Version January 1996. [3] P. Bergveld, Development of an ion-sensitive solid-state device for neurophysical measurements, short communication, IEEE Trans. Bio-Med. Eng. 17 (1970) 70 – 71. [4] P. Bergveld, Development, operation and application of the ISFET as a tool for electrophysiology, IEEE Trans. Bio-Med. Eng BME-19 (5) (1972) 342 – 351. [5] T. Matsuo, M. Esashi, Methods of ISFET fabrication, Sensors and Actuators 1 (1981) 77 – 96. [6] J. Janata, R.J. Huber, Solid-State Chemical Sensors, Academic, New York, 1985. [7] B. Pala´n, VLSI Integration of the BARMINT Sensor Interface Module, TIMA technical report, Grenoble, France, 1996. [8] E. Seevinck, R.F. Wassenaar, A versatile CMOS linear transconductor/square-law function circuit, IEEE J. Solid-State Circuits SC-22 (6) (1987) 366 – 377. [9] D. Esteve, BARMINT-Basic Research for Microsystems Integration, Cepadues-Editions, Toulouse, France, 1997.
Acknowledgements This research has been conducted at the TIMA Laboratory, INPG, Grenoble, France. The authors would like to thank to CNM foundry, Barcelona, Spain, for the fabrication of the ISFET sensor interface.
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B. Pala´n et al. / Sensors and Actuators B 57 (1999) 63–68
Biographies Bohusla6 Pala´n graduated in Microelectronics from the FEE CTU Prague in 1997. From 1996 he joined the TIMA Laboratory, Grenoble, to work with analog IC design and tests of ISFET and pressure sensor interfaces within the ESPRIT III European project. He is a Ph.D. student at the Department of Microelectronics, Faculty of Electrical Engineering, CTU Prague. His research includes chemical and biochemical sensors, analog ASIC design and applications in the field of microsystems. Filipe Vinci dos Santos received his Electronics engineering degree from the Federal University of Rio de Janeiro/COPPE in 1989, and his M.Sc. degree in Microelectronics in 1992, from the same university. From 1992 to 1994 he was at the Solid State Detector Development Group of CERN (European Laboratory for Particle Physics)/Geneva, developing solid-state radiation imaging systems for biomedical applications. Currently he works at TIMA-Grenoble, in the MicroSystems Group, where he researches radiationhard circuits and circuit hardening techniques, for space systems, as part of his doctorate work. He also conducts research in analog interface circuitry for integrated microsystems, high-temperature circuit design and analog circuit testing and testability. Jean-Michel Karam is the MicroSystems Group Leader at TIMA Laboratory, where he is responsible for the CMP’s microtechnology development activities.
.
He received the Ph.D. degree in Microelectronics from the National Polytechnic Institute of Grenoble, the Advanced Studies degree in Microelectronics from the University of Paris, and the Engineer degree from the Ecole Supe´rieure d’Inge´nieurs de Beyrouth. He has served on many conference program committees and has guest-edited two special issues of Microelectronics Journal. He is an IEEE member. Bernard Courtois is the director of TIMA Laboratory, where he researches computer-aided design, architecture, and testing of integrated circuits and systems. He is also the director of CMP Service. He received the Engineer degree in 1973 from the Ecole Nationale Supe´rieure d’Informatique et de Mathe´matiques Applique´es de Grenoble, and the Doctor-Engineer and Doctor of Sciences degrees from the National Polytechnic Institute of Grenoble. Dr Courtois served as general chair of EDAC-EuroASIC 1993 and program cochair of EDAC-ETC-EuroASIC 1994. He is a member of the IEEE. Mirosla6 Husa´k graduated in Radioengineering from the Faculty of Electrical Engineering, CTU in Prague. He received Ph.D. degree in 1985. From 1978 to 1984 he was working as a research fellow in the area of device physical modeling in the Department of Microelectronics. In 1984 he joined the staff of the Department as an Assistant Professor. He is working in the field of design and application of sensors, sensor systems and microsystems. He is the Head of the Department.
New ISFET sensor interface circuit for biomedical applications B. Pala´n b,*, F.V. Santos a, J.M. Karam a, B. Courtois a, M. Husa´k b b
a TIMA Laboratory, 46 a6enue Fe´lix Viallet, Grenoble, France Department of Microelectronics, Czech Technical Uni6ersity in Prague, Faculty of Electrical Engineering, Technicka´ 2, 166 27 Prague 6, Czech Republic
Received 16 October 1998; received in revised form 29 January 1999; accepted 8 February 1999
Abstract This article presents a novel architecture of an ISFET sensor interface circuit, monolithically integrated on a 3D MCM, part of a biomedical microsystem. It is a differential configuration with two ISFET devices (one with Si3N4 ion sensitive layer, the other with SiO2 sensitive layer) and realized in a 2.5 mm CMOS technology. The sensor interface is simple, has a current output signal and low silicon area requirements. The circuit architecture provides digital facilities, which makes possible the performance of the configuration been optimized during a calibration step of the system. © 1999 Elsevier Science S.A. All rights reserved. Keywords: ISFET sensor; Analog ASIC design; ISFET sensor interface
1. Introduction The desirable property of a microsystem for medical applications is to realize chemically sensitive sensors with conventional IC technologies that have very small dimensions and fast response. This article presents a novel architecture of an ISFET sensor interface circuit which has been integrated as a part of a sensor module of a biomedical microsystem. This chip contains also several other sensors, for measuring temperature and pressure of the incoming liquid [1], in addition to the ISFET-based pH sensors. Two ISFET devices and the differential analog interface are monolithically integrated, using a 2.5 mm CMOS technology from CNM, Barcelona, Spain [2]. The interface is optimized for use in the medical microsystem which implies the restrictions to the CMOS process and a low power consumption. As sensors often have unpredictable specifications, a high degree of flexibility is also required for the sensor interface. In that way, the characteristics can be adapted to the actual specifications of the sensor. The analog interface circuit proposed for the sensors is equipped with digital con* Corresponding author. Tel.: + 33-4-76574770; 76473814. E-mail address: [email protected] (B. Pala´n)
fax:
+33-4-
trol facilities for both addressing and adapting their characteristics. A voltage-to-current (V–I) converter generates a current output because of its perfectly integration to the A/D converter (current input oversampling sigma–delta) selected for the microsystem. 2. ISFET sensors The principle of measuring the concentration of chemical quantities with a solid-state device, called ISFET, was introduced in 1970 by P. Bergveld [3]. The first reported ISFETs were devices with a SiO2 gate insulating layer [4]. Because of its hydrating and highly unstable properties, the possibility of using other ionsensitive materials (Si3N4, Al2O3, Ta2O5) was very soon an object of research. Each layer has some important properties, influencing the ISFET’s performance. These properties are sensitivity, selectivity, long-term drift, response time and temperature dependency. A good summary of chemical response of various fabricated pH ISFETs was given in Matsuo and Esashi [5]. When ISFET and CMOS compatibility is desired, silicon nitride is the best choice as a sensitive membrane due to its sensitivity, long term stability and high resistance to hydration. Si3N4 is also a well known material in microelectronics and it is extensively used in CMOS technology.
0925-4005/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved. PII: S 0 9 2 5 - 4 0 0 5 ( 9 9 ) 0 0 1 3 6 - 7
B. Pala´n et al. / Sensors and Actuators B 57 (1999) 63–68
64
Fig. 1. (a) CNM ISFET sensor layout, and (b) the ISFET model including drain and source series resistances.
Fabrication of ISFET of different sensitivities is necessary for the proper operation of a differential configuration. Both our sensors are active and monolithically integrated together with the sensor interface. One ISFET is covered by a Si3N4 sensitive layer, the second one is covered only with a SiO2 layer. The second ISFET is much poorer [5], with significant non-linearity, but it can be used to demonstrate the circuit function and technology compatibility. A physical layout of one ISFET is shown in Fig. 1a. The dimensions of the sensor gate are 400/20 mm. The L must be at least 20 mm, to insure a good contact with the liquid at the gate, and W must be at least 400 mm for an acceptable transistor b. The reference electrode (Pt type) is not shown in the layout. Fig. 1b illustrates an ISFET electrical model including source and drain series resistances. In the configuration of the ISFET sensor, the electrical contacts to the drain and source are not close to the actual transistor drain and source terminals. In practice, the area surrounding the gate is completely covered with protecting and insulating layers and in the vicinity of this region, no metal contacts can exist, so the contact places are usually some millimeters away. In this case, the ISFET internal drain and source resistances for the structure in Fig. 1a are
Table 1 Properties of used ISFET sensors Device
ISFET1
ISFET2
Sensitive layer Sensitivity DVth Size of sensor’s gate W/L Vt0 (zero-bias)
Si3N4 52–58 mV/pH 400/20 mm −2.9 V
SiO2 24–36 mV/pH 330/20 mm −2.9 V
about 100 V. Because these series resistances seriously influence the ISFET’s electrical behaviour, they should be taken into account in the ISFET model. Moreover, a parasitic capacitances drain-substrate, source-substrate of several tens of pF have to be added to the ISFET simulation model. Table 1 summarizes properties of both used sensors.
3. Sensor interface design In general, single ISFET interface circuits do not offer any degree of compensation for temperature dependency or long-term drift. Therefore, several ISFET differential configurations have been studied. The difference is taken at the output signals of two ISFETs implemented in the same solution and using the same reference electrode. Temperature dependency as well as common noise compensation can be reduced to a certain level. Instability caused by the membrane layers of the ISFETs and the unstable electrolyte-reference electrode potential problem will be also solved. The global sensor interface configuration is presented in Fig. 2. It consists of two source-and-drain follower circuits and a voltage-to-current converter. The reference electrode is grounded since a sample liquid can be conductive and metallic parts of the microsystem will be probably grounded also. Two identical read-out circuits are used for each ISFET sensor, as shown in Fig. 2 (see subcircuit in a dashed line). The drain current of the ISFET1 (ISFET2) is driven by the current sink Is2 (Is22) and the drain-source voltage Vds is fixed by the current source Is1 (Is11) and resistor RsetA (RsetB) [6]. A change in ion activity will lead to a change of the common mode level of Vds with respect to ground. Both ISFETs work in the
B. Pala´n et al. / Sensors and Actuators B 57 (1999) 63–68
65
Fig. 2. Differential ISFET sensor interface scheme.
Fig. 3. Simulation plot of two ISFET source-and-drain followers, pH sweep, at room temperature.
linear region. When Vg =0V and Vgs = −Vs = −VoutA, the expression for VoutA is derived as: VoutA = − Vth −
Is2 I ·R − s1 setA b·Is1·RsetA 2
(1)
When b, RsetA, Is1 and Is2 are constants, VoutA is proportional to a change in ion activity ai represented by the threshold voltage Vth of the ISFET1 sensor. VoutB signal can be obtained similarly. Identical current sources Is1 and Is11 have been designed using the cascode current source architecture with 20 mA currents [7]. Low voltage cascode current sinks Is2, Is22 have been designed to have also the same quiescent currents of 55 mA. Both RsetA, RsetB from Fig. 2 are made as P+ diffusions in N-wells to form 10 kV resistors. The
same approach is applied with the design of four voltage followers A1, A11 (A2, A22). All followers have been realized with PMOS input transistors with the maximum offset of 2 mV, and able to drive 200 pF capacitive load (ISFET’s drain and source parasitic capacitances). Linear V–I converter with differential PMOS inputs has been designed based on the first-order square-law characteristics of MOS transistors biased in saturation [8] to have the transconductance constant Iout/Vin = 5 mA/0.1 V. Voltage supplies for all the interface were applied to Vdd = 5 V and VdH = 6 V (for V–I converter). Simulation plot of two ISFET source-and-drain voltage follower circuits presents Fig. 3. The total current output response of the differential ISFET interface represents Fig. 4.
B. Pala´n et al. / Sensors and Actuators B 57 (1999) 63–68
66
Simulated results showed that this analog interface would be able to measure pH concentration with the precision of 9 0.15 pH. A microphotograph of the fabricated sensor circuit is shown in Fig. 5.
4. Results and discussion An extended set of electrical and pH tests have been carried out in order to prove the proper circuit functionality. Firstly, electrical characterization programme has been prepared. The input offset of maximum 2 mV has been measured within the input voltage range from 0.4 to 2.8 V of all voltage followers. Low voltage cascode current sinks work from 0.4 V. The cascode current sources operate up to 3 V. The linear V–I converter has the tranconductance constant about Iout/ Vin =5 mA/0.1 V as it has been designed. The measured signal at the output of the V – I converter compared with the simulation plot presents Fig. 6.
Secondly, five buffer solutions have been applied for pH tests (pH 4.01; 6.86; 7.00; 9.18; and 10.01). An external Fe microprobe needle has been used as a reference electrode (technology difficulties of Pt electrode integration on the chip). The measurements were done in the dark and with permanent stirring of the liquid. Unfortunately, the ISFET2 sensor has been found inactive with the grounded reference electrode due to a technological error [9] (its zero-bias threshold voltage has been set to Vto = + 0.6 V than was required in Table 1), and thus the VoutB signal approached zero. Only VoutA signal has been successfully recorded and shown in Fig. 7. The measured signal can be compared with its simulation from Fig. 3. It is shifted up about + 0.7 V because of the other reference electrode potential. Even though the differential configuration has not been fully tested during the pH measurements, the feasibility and functionality of the ISFET sensor circuit has been verified.
Fig. 4. Total simulation plot of the ISFET sensor interface at room temperature, pH sweep.
Fig. 5. Die microphotograph of the all monolithic differential ISFET sensor interface.
B. Pala´n et al. / Sensors and Actuators B 57 (1999) 63–68
67
Fig. 6. Measured result at the current output.
Fig. 7. VoutA output signal as function of the pH concentration at room temperature.
5. Conclusions
References
This paper described design and tests of the novel ISFET sensor interface, a part of a biomedical microsystem. The CMOS differential configuration with two ISFETs includes two source-and-drain follower circuits and the V– I converter. Temperature dependency of the ISFETs can be minimized by choosing an optimal value for the current sinks and sources during a calibration step of the system. Differential configuration is adaptable for each ISFET device. It can become a suitable sensor interface for biomedical applications.
[1] R. Wissing, J.M. Karam, Design of the Integrated Electronics for the BARMINT Medical Demonstrator, TIMA technical report, Grenoble, France, 1995. [2] Design Rules and SPICE Parameters for the CMOS CNM25 Technology, CNM, Barcelona, Spain Version January 1996. [3] P. Bergveld, Development of an ion-sensitive solid-state device for neurophysical measurements, short communication, IEEE Trans. Bio-Med. Eng. 17 (1970) 70 – 71. [4] P. Bergveld, Development, operation and application of the ISFET as a tool for electrophysiology, IEEE Trans. Bio-Med. Eng BME-19 (5) (1972) 342 – 351. [5] T. Matsuo, M. Esashi, Methods of ISFET fabrication, Sensors and Actuators 1 (1981) 77 – 96. [6] J. Janata, R.J. Huber, Solid-State Chemical Sensors, Academic, New York, 1985. [7] B. Pala´n, VLSI Integration of the BARMINT Sensor Interface Module, TIMA technical report, Grenoble, France, 1996. [8] E. Seevinck, R.F. Wassenaar, A versatile CMOS linear transconductor/square-law function circuit, IEEE J. Solid-State Circuits SC-22 (6) (1987) 366 – 377. [9] D. Esteve, BARMINT-Basic Research for Microsystems Integration, Cepadues-Editions, Toulouse, France, 1997.
Acknowledgements This research has been conducted at the TIMA Laboratory, INPG, Grenoble, France. The authors would like to thank to CNM foundry, Barcelona, Spain, for the fabrication of the ISFET sensor interface.
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B. Pala´n et al. / Sensors and Actuators B 57 (1999) 63–68
Biographies Bohusla6 Pala´n graduated in Microelectronics from the FEE CTU Prague in 1997. From 1996 he joined the TIMA Laboratory, Grenoble, to work with analog IC design and tests of ISFET and pressure sensor interfaces within the ESPRIT III European project. He is a Ph.D. student at the Department of Microelectronics, Faculty of Electrical Engineering, CTU Prague. His research includes chemical and biochemical sensors, analog ASIC design and applications in the field of microsystems. Filipe Vinci dos Santos received his Electronics engineering degree from the Federal University of Rio de Janeiro/COPPE in 1989, and his M.Sc. degree in Microelectronics in 1992, from the same university. From 1992 to 1994 he was at the Solid State Detector Development Group of CERN (European Laboratory for Particle Physics)/Geneva, developing solid-state radiation imaging systems for biomedical applications. Currently he works at TIMA-Grenoble, in the MicroSystems Group, where he researches radiationhard circuits and circuit hardening techniques, for space systems, as part of his doctorate work. He also conducts research in analog interface circuitry for integrated microsystems, high-temperature circuit design and analog circuit testing and testability. Jean-Michel Karam is the MicroSystems Group Leader at TIMA Laboratory, where he is responsible for the CMP’s microtechnology development activities.
.
He received the Ph.D. degree in Microelectronics from the National Polytechnic Institute of Grenoble, the Advanced Studies degree in Microelectronics from the University of Paris, and the Engineer degree from the Ecole Supe´rieure d’Inge´nieurs de Beyrouth. He has served on many conference program committees and has guest-edited two special issues of Microelectronics Journal. He is an IEEE member. Bernard Courtois is the director of TIMA Laboratory, where he researches computer-aided design, architecture, and testing of integrated circuits and systems. He is also the director of CMP Service. He received the Engineer degree in 1973 from the Ecole Nationale Supe´rieure d’Informatique et de Mathe´matiques Applique´es de Grenoble, and the Doctor-Engineer and Doctor of Sciences degrees from the National Polytechnic Institute of Grenoble. Dr Courtois served as general chair of EDAC-EuroASIC 1993 and program cochair of EDAC-ETC-EuroASIC 1994. He is a member of the IEEE. Mirosla6 Husa´k graduated in Radioengineering from the Faculty of Electrical Engineering, CTU in Prague. He received Ph.D. degree in 1985. From 1978 to 1984 he was working as a research fellow in the area of device physical modeling in the Department of Microelectronics. In 1984 he joined the staff of the Department as an Assistant Professor. He is working in the field of design and application of sensors, sensor systems and microsystems. He is the Head of the Department.