Design of a single-chip pH sensor using a conventional 0.6-μm CMOS process (original) (raw)
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Design of a Single-Chip pH Sensor Using a Conventional 0.6-$muhbox m$CMOS Process
IEEE Sensors Journal, 2004
A pH sensor fabricated on a single chip by an unmodified, commercial 0.6-m CMOS process is presented. The sensor comprises a circuit for making differential measurements between an ion-sensitive field-effect transistor (ISFET) and a reference FET (REFET). The ISFET has a floating-gate structure and uses the silicon nitride passivation layer as a pH-sensitive insulator. As fabricated, it has a large threshold voltage that is postulated to be caused by a trapped charge on the floating gate. Ultraviolet radiation and bulk-substrate biasing is used to permanently modify the threshold voltage so that the ISFET can be used in a battery-operated circuit. A novel post-processing method using a single layer of photoresist is used to define the sensing areas and to provide robust encapsulation for the chip. The complete circuit, operating from a single 3-V supply, provides an output voltage proportional to pH and can be powered down when not required.
Procedia Chemistry, 2012
In this work, we show that by using Metal-Insulator-Metal (MIM) structures integrated in series to the gate of submicron Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) devices, highly-sensitive and ultra-low power consumption pH sensors can be obtained. One MIM capacitor enables external polarization of the MOSFET device while a second MIM capacitor is connected to a sensing plate whose surface is whether a thick polyimide layer or the last metallization level. The electrochemical response of these surfaces to pH buffer solutions resembles that of Ion-Sensitive Field-Effect Transistor (ISFET) devices whose pH sensitivity is dependent on the type of surface material being exposed.
ISFET pH sensor characterization: towards biosensor microchip application
2004
The ion-sensitive field effect transistor (ISFET) based pH sensor has the advantages of smaller size, fast response time and fabrication compatible with standard MOS technology. Beside that, the functionality of pH ISFETs is various especially in biomedical areas. In the design and characterization of an ISFET pH sensor, the ISFET model was characterized and a final design has been evolved with the assistance of the Tanner tools software. To provide a better understanding of pH ISFET as a biosensor, the C-V characteristics, temperature dependence of the ISFET and pH sensitivity of Electrolyte-Insulator-Semiconductor in response to different pH are examined. The insulator, Aluminium oxide (Al 2 O 3 ) has been applied as a pH sensitive layer. The ISFET is matched with a metal oxide field effect transistor (MOSFET) at the differential input stage of a CMOS operational amplifier and realized in a 0.8 um CMOS technology. From the output of ISFET operational amplifier, the pH sensitivity is approximately 54.8 mV per pH.
A p H-ISFET based micro sensor system on chip using standard CMOS technology
A monolithic pH sensor system has been studied and developed, based on standard CMOS technology. The micro system includes an on-chip integration of differential ISFET/REFET sensing devices, metal constructed pseudo reference electrode (PRE) and front-end measurement electronics. A post CMOS process flow is devised in our laboratory to allow the ISFET to be fabricated in a standard CMOS foundry with minimal modifications. The chip has been realized with Chartered Semiconductor's 0.35µm, 4-metal and 2-poly layer CMOS process and operates at 3.3V. The total die area is 5mm 2 .Thanks to the on-chip signal conditioning; the micro sensor system achieves a superior sensitivity of 53.67mV/pH as well as an enhanced linearity. Hence, it demonstrates the possibility of embedding ISFET based micro sensor arrays in advanced digital, analog and mixed signal VLSI for the intelligent measurement required in various chemical, biochemical and biomedical applications.
Solid State Circuits Technologies, 2010
Solid State Circuits Technologies 422 drawbacks on ISFET continuous-mode monitoring applications. Furthermore, the conventional floating-source constant-voltage and constant-current circuit (Caras & Janata, 1980) in Fig. 2 faces problems including noise interference, requirement of two external current sources and body effect. In order to solve the aforementioned problems, this chapter focuses on developing a series of improved readout circuit techniques that enhances the performance of ISFET and demonstrates their pH sensing capability for environmental monitoring. The current status and main ISFET-based Research Biosensor development Micro-system in a standard CMOS technology Single and sensor array applications Fabrication technology and device design Readout circuit development Non-ideal characteristics study and compensation How to reference
ISFET pH Sensitivity: Counter-Ions Play a Key Role
Scientific Reports, 2017
The Field Effect sensors are broadly used for detecting various target analytes in chemical and biological solutions. We report the conditions under which the pH sensitivity of an Ion Sensitive Field Effect transistor (ISFET) sensor can be significantly enhanced. Our theory and simulations show that by using pH buffer solutions containing counter-ions that are beyond a specific size, the sensor shows significantly higher sensitivity which can exceed the Nernst limit. We validate the theory by measuring the pH response of an extended gate ISFET pH sensor. The consistency and reproducibility of the measurement results have been recorded in hysteresis free and stable operations. Different conditions have been tested to confirm the accuracy and validity of our experiment results such as using different solutions, various oxide dielectrics as the sensing layer and off-the-shelf versus IC fabricated transistors as the basis of the ISFET sensor.
A signal processing ASIC for ISFET-based chemical sensors
Microelectronics Journal, 2004
With the advantages of small size, reliability, rapid response, compatibility to standard CMOS technology and on-chip signal processing, Ion-Sensitive Field Effect Transistor (ISFET)-based transducers are increasingly being applied in physiological data acquisition and environment monitoring. This paper presents a signal processing Application Specific Integrated Circuit (ASIC) and a discrete temperature compensation chip design of a potentiometric ISFET-based chemical sensor. To assure the measurement of a correct pH value, the two-point calibration circuitry based on the response of standard pH 4 and 7 buffer solution has been implemented by using Algorithmic State Machine hardware algorithms. For battery power consideration, the proposed signal processing ASIC consisting of low voltage (3 V) mixed signal modules has been developed and fabricated in a 0.5 mm CMOS technology. The results demonstrate small differences of pH response of ISFET's operating with and without ASIC device, i.e. only the order of 0.1 mV/pH with respect to sensitivity. Furthermore, using the temperature compensating circuitry reduces the ISFET temperature coefficient to þ0.15 mV/8C, and hence results in a lower pH value variation of 20.0023 pH/8C. It was shown that more accurate pH measurement can be concluded with the proposed ASIC and V T extractor circuitry.
Ultrahigh-Sensitive CMOS pH Sensor Developed in the BEOL of Standard 28 nm UTBB FDSOI
IEEE Journal of the Electron Devices Society, 2018
This paper reports ultrahigh-sensitive and ultralow-power CMOS compatible pH sensors that are developed in the back-end-of-line (BEOL) of industrial 28-nm ultrathin body and buried oxide (UTBB) fully depleted silicon-on-insulator (FDSOI) transistors. Fabricating the sensing gate and the control gate of the sensors in a capacitive divider circuit, CMOS compatible pH sensors are demonstrated where the front gate bias is applied through a control gate rather than a bulky reference electrode. On the other hand, the strong electrostatic coupling between the front gate and the back gate of FDSOI devices provide an intrinsic signal amplification feature for sensing applications. Utilizing an atomic layer deposited aluminum oxide (Al 2 O 3) as a pH sensing film, pH sensors having a sensitivity of 475 mV/pH and 730 mV/pH in the extended gate and BEOL configuration, respectively, are reported. Sensitivities of both configurations are superior to state-of-the-art low power ion-sensitive field-effect transistors. The small sensing area and the FDSOI-based low power technology of the device make the sensors ideal for the IoT market. The proposed approach has been validated by TCAD simulation, and demonstrated through experimental measurements on proof-of-concept extended gate pH sensors and on sensors that are developed in the BEOL of industrial UTBB FDSOI devices. INDEX TERMS Aluminum oxide, back-end-of-line (BEOL), capacitive coupling, extended gate, fullydepleted silicon-on-insulator (FDSOI), ion-sensitive field-effect transistor (ISFET), pH sensor.
Investigation of Metrological Performance of the ISFET-Based pH Sensors
The metrological performance characteristics of the dual channel p-type ISFET pH sensors with silicon nitride sensitive layer are investigated. The simplified three-lead sensor design and corresponding signal readout circuit are employed and the sensor transform function is evaluated as dependency of the ISFET channel current on the analyzed solution pH. It is shown that achievable pH measurement accuracy is sufficient for use of the developed sensors in typical laboratory applications in either single channel or differential mode of operation, as alternative to the traditional glass electrodes.