Wen-Yaw Chung

Study on separative structure of EnFET to detect acetylcholine

Abstract In this study, our laboratory used a separative structure of extended gate field effect transistor (EGFET) to detect pH value and constructed an enzyme modified field effect transistor (EnFET) by coupling them with a membrane containing immobilized acetylcholinesterase (AcChE). The enzyme-catalyzed hydrolysis reaction of acetylcholine seemed to be resulted in the pH change of the membrane due to the formation of acetic acid. This structure has a lot of advantages, such as being insensitive toward light, being simple to in its passivation and package, and the flexibility of shape in the extended gate area, etc. In addition, it is easier to fabricate and package the sensors, and the measurement is simple for the application of disposable biosensor.

Study of amorphous tin oxide thin films for ISFET applications

Abstract In this study, an amorphous tin oxide (SnO 2 ) obtained by thermal evaporation was used as a pH-sensitive material for pH-ISFETs. Capacitance–voltage (C–V) curves of the EIS diode were used to evaluate pH response of SnO 2 thin film. Subsequently, SnO 2 /SiO 2 gate ISFET was fabricated and pH sensitivity was determined through a shift in the threshold voltage of an ISFET sensor. The experimental data show that the SnO 2 /SiO 2 gate ISFET sensors have a linear pH response of about 58 mV pH −1 in a concentration range between pH 2 and pH 10. In addition, the other characteristics of this sensor, such as temperature effect, drift effect, hysteresis and response time were also investigated in this paper.

Titanium Nitride Membrane Application to Extended Gate Field Effect Transistor pH Sensor Using VLSI Technology

A new process for the fabrication of the extended gate field effect transistor (EGFET) together with complementary metal oxide semiconductor (CMOS) circuits on the same chip is reported. The sensing membrane of the EGFET is titanium nitride (TiN) conducting material and it is fabricated using the r.f. sputtering method. The chips are fabricated using the standard submicron 0.5 µm double poly double metal (DPDM) N-well CMOS IC process. No extra mask is used in the post-process. An instrument amplifier circuit is described that provides an output voltage dependent on the threshold-voltage variations in the sensing membrane. According to the experimental results, the high linear sensitivity approaches 57 mV/pH. The hysteresis voltage is 0.5 mV per cycle of buffer solutions of pH7→pH4→pH7→pH10→pH7. This structure is also insensitive to light. This EGFET is fabricated using the standard technology and no difficulty is experienced in realizing this multi species device. The EGFET and readout circuits are produced using VLSI technology, achieving reduced area and low cost. This device has the advantages of mass production.

Study on pHpzc and surface potential of tin oxide gate ISFET

Abstract In this study, capacitance–voltage (C–V) and current–voltage (I–V) measurements were used to investigate pHpzc (point zero of charge) and surface potential of a tin oxide gate ISFET. Dual FETs configuration: Al/SnO2/Si3N4/SiO2 gate MOSFET and SnO2/Si3N4/SiO2 gate ISFET were fabricated for this study. Experimental results show that different operations of ISFETs will yield different values of the pHpzc and surface potential. For example, the pHpzc is 5.6 for the ISFETs operation at the flat band condition and the pHpzc is 6 for the ISFETs operation at the linear region. This phenomenon can be explained by the influence of charge density at the semiconductor–insulator interface. Additionally, according to a series of theoretical simulations, we can conclude that the surface parameter ΔpK is the dominated factor of pH response in ISFET. Experimental results and theoretical simulations can achieve a good curve fitting when appropriate surface parameters for tin oxide are chosen.

Characteristics of silicon nitride after O/sub 2/ plasma surface treatment for pH-ISFET applications

Silicon nitride (Si3N4) sensing gate pH-ion-selective field effect transistors (ISFETs) were treated by 2.54-GHz microwave O2 plasma, the results show the ISFET sensitivity has an advantage up to 24% increment after the plasma treatment. Electron spectroscopy for chemical analysis (ESCA) is used to make sure that the plasma treatment is not just a native oxide cleaning procedure. The samples, which were immobilized with glutaraldehyde used as a bifunctional reagent and 3-aminopropyItriethoxysilane used as an adhesion promoter were studied. The binding force between the glucose oxidase and glutaraldehyde immobilized samples, and the element concentrations of nitrogen in 3-aminopropyltriethoxysilane immobilized samples are higher which were treated by plasma.

A 600 μW readout circuit with potentiostat for amperometric chemical sensors and glucose meter applications

This paper presents a low power electrochemical interface circuit for amperometric sensors. The readout circuit with potentiostat design maintains a constant bias potential between the reference and working electrodes using one operational transconductance amplifier (OTA) and four MOS transistors. Redox currents from 1 to 50 μA can be measured by the readout circuit with maximum nonlinearity of plusmn1 percent over the aforementioned range. The micro instrument has been implemented in 0.35 μm TSMC CMOS technology that consumes only 600 μW of power and occupies a small area of 0.16 mm2. Chip test results emulate the simulation results with good agreement and confirm the effectiveness of the designed system.

Multi-structure ion sensitive field effect transistor with a metal light shield

Abstract It is known that light sensitivity in ion sensitive field effect transistors (ISFETs) during illumination is due to carrier generation in the silicon substrate. In order to improve this drawback, multi-structure ISFETs: tin oxide/Al/insulator/Si ISFET devices are investigated in this study. In this structure, aluminum is used as a light shield, and the tin oxide is used as a pH sensitive layer. We have developed SnO 2 /Si 3 N 4 /SiO 2 /Si ISFETs and SnO 2 /Al/Si 3 N 4 /SiO 2 /Si ISFETs, respectively. The pH sensitivity of these devices was measured and the data shows that the SnO 2 /Al/Si 3 N 4 /SiO 2 /Si ISFET sensors have a linear pH response of about 56–58 mV/pH in a concentration range between pH2 and pH10 under room light conditions. Subsequently, the light sensitivity of the ISFETs with/without aluminum as a light shield were investigated under 2000 lx white light exposure. The data show that ISFETs with aluminum as a light shield have low light sensitivity compared with ISFETs without aluminum as a light shield.

Temperature and optical characteristics of tin oxide membrane gate ISFET

The influence of temperature and optical effects on ISFET performance are important. In this study, the temperature characteristics of the SnO/sub 2//Si/sub 3/N/sub 4//SiO/sub 2//Si ISFET are investigated by the zero temperature coefficient (T.C.) adjustment and the dual FETs configuration, respectively. The result show that a zero T.C. of the SnO/sub 2/ gate ISFET can be achieved when the appropriate operation current was set. Subsequently, the T.C. of tin oxide membrane/electrolyte interface can be evaluated by the dual FETs configuration. On the other hand, due to the SnO/sub 2/ gate ISFET is sensitive to the light exposure, thus in order to improve this drawback, a multi-structure ISFETs: SnO/sub 2//Al/SiO/sub 2//Si/sub 3/N/sub 4//Si ISFETs have been developed. In this structure, aluminum is used as a light shield, and the tin oxide is used as a pH sensitive layer. The results show the ISFETs with aluminum as a light shield have low light sensitivity compared with ISFETs without aluminum as a light shield.

The influence of isothermal annealing on tin oxide thin film for pH-ISFET sensor

Abstract The aim of this paper is to investigate pH sensitivity of tin oxide thin films prepared by thermal evaporation, and the influences of isothermal annealing on its characteristics. A series of capacitance–voltage (C–V) curves of SnO2/SiO2/Si electrolyte insulator semiconductor (EIS) diodes are used to evaluate pH sensitivity of tin oxide thin films. The results show that tin oxide thin films (as grown) have linear pH sensitivities of approximately 58 mV/pH in a concentration range between pH 2 and pH 10. However, pH sensitivity decreases after the isothermal annealing processes at 300°C, 400°C, and 500°C in N2 ambiance for 1 h; and pH sensitivity goes further down to only 33 mV/pH, after annealing in N2 ambiance for 15 h. This phenomenon influences the structure of tin oxide thin films, which will undergo phase transition from amorphous to polycrystal after the isothermal annealing process. Moreover, the characteristics of the tin oxide gate ion-sensitive field-effect transistor (ISFET) (SnO2/SiO2 gate ISFET), where the tin oxide is formed under optimum condition, is also presented in this paper.

Analog integrated circuit design for the wireless bio-signal transmission system

This paper presents an analog-signal processor chip design for its application on the wireless bio-signal transmission system. The processor is used to handle the physiological signal such as the electrocardiography (ECG), electroencephalography (EEG), or the electromyography (EMG), and so on. All analog blocks in the processor chip are realized in a 0.5 /spl mu/m double-poly and double-metal CMOS technology. The measured results show the processor chip can capture the bio-signal with the frequency range of 0.5 Hz to 220 Hz, and has a total voltage gain of 54 dB, good agreement has been found between computer simulation and measured performance. Compared to the on-board prototype system, on-chip processor system can minimize the hardware area and reduce the product cost.