KEYWORDS: Near field diffraction, Diffraction, Far-field diffraction, Near field optics, Image quality, Convolution, Bessel functions, Optical engineering, Near field, Photomasks
The sensitivity and hysteresis effects of ion-sensitive fieldeffect
transistor (ISFET) devices based on a-WO3, Ta2O5 , and a-Si:H
thin films have been investigated. The pH sensitivity is one of the important
characteristic parameters of ISFET devices, and the response of an
ISFET is mainly determined by the type of the sensing membrane; therefore
the sensing material plays a significant role. Furthermore, hysteresis
leads to inaccuracy and instability of ISFET measuring devices. In this
investigation the pH sensitivities of different sensing-gate ISFET devices
were measured in different buffer solutions by current-voltage (I -V)
measurement, and the hysteresis curves were measured by exposing
the device to several cycles of pH values over different loop times. According
to the experimental results, a-WO3 and a-Si:H are useful in
acidic buffer solutions (pH 1 to 7), and Ta2O5 at pH 1 to 12. The pH
sensitivities are all larger than 50 mV/pH, and it was found that the key
parameter in determining the hysteresis width is the loop time.
The temperature effect is an important factor for the deviation of the pH-ISFET (ion sensitive field effect transistor). In this paper, we use the SnO2 as the pH sensing membrane to investigate the temperature characteristics of the pH-ISFET. The SnO2 membrane was prepared by the sol-gel technology. We use the tin (II) chloride dihydrate (SnCl2(DOT)2H2O) and ethanol to synthesize the sol of the SnO2 thin film. For the sol-gel prepared SnO2, the cost is lower than other methods.The Keithley 236 instrument was used to measure the IDS - VG curves of the SnO2 gate pH-ISFET for different pH buffer solutions form ranging temperature 15 degree(s)C - 45 degree(s)C. According to the experimental results we can obtain the sensitivities for different operation temperatures. The sensitivity is increased with increasing temperature. The TCS (temperature coefficient of the sensitivity) is also calculated.
In the pH-ISFET (ion sensitive field effect transistor) applications, the temperature is one of the important factors for the stability. The hydrogenated amorphous carbon (a-C:H) films is used for the sensitive layer of the pH-ISFET. The a- C:H pH-ISFET device is prepared by the plasma-enhanced low pressure chemical vapor deposition (PE-LPCVD). The thickness of the a-C:H was 2000 Angstrom, and the a-C:H gate pH-ISFET was encapsulated by epoxy. The Keithley 236 instrument was used to measure the IDS - VGS curves of the a-C:H gate pH-ISFET in the various pH buffer solutions at 15 degree(s)C - 55 degree(s)C. According to the experimental results, we found the sensitivity of the a-C:H gate pH-ISFET is increased with the temperature. Finally, the TCS (temperature coefficient of sensitivity) can also be calculated.
In this paper, the sol-gel prepared SnO2 thin film is first applied for the pH sensing. We use the SnCl2(DOT)2H2O as the precursor. It is cheaper than other methods. The resulting solution is dropped on the gate of the SiO2 gate pH-ISFET (ion sensitive field effect transistor). After baking, the thin film will convert to SnO2. We also use the thermal evaporation system to prepare the SnO2 gate MOSFET. Then, we use the Keithley 236 instrument to measure the IDS-VG curves of the SnO2 gate MOSFET and pH-ISFET for the different pH buffer solutions. Since the MOSFET and pH-ISFET are fabricated on the same silicon wafer, the properties of these devices are identical. Therefore, we can use the experimental results and theoretical model of the pH-ISFET to find the pH sensitivity and pHPZC (pH at the point of zero charge) of the sol-gel prepared SnO2 gate pH-ISFET, which are about 57.36 mV/pH and 11.3, respectively.
The hydrogenated amorphous carbon (a-C:H) contains significant fractions of sp3 type C bondings, giving them attractive physical and mechanical properties, some similar to a certain extent to the diamond. Otherwise, the dielectric constant of the a-C:H films covers the range of 2.5 - 6, and the a-C:H also can be used for the protective and isolated layer. In this paper, we study the sensitivity of the a-C:H applied to the pH-ISFET (ion sensitive field effect transistor). The a- C:H gate pH-ISFET devices were prepared by the plasma-enhanced low pressure chemical vapor deposition (PE-LPCVD). The sensitivity is determined by the IDS - VGS and C-V curves shift in the various pH buffer solutions. We can also measure the pH at zero charge point (pHpzc) for the a-C:H gate pH-ISFET.
In application of the pH-ISFET, the hysteresis and temperature effects are two important influences of accuracy. There have been many studies about the above subjects, however, the hysteresis behaviour will change with the temperature and affect the reproducibility of the devices. Hence, we study the temperature dependence of the hysteresis behaviour for the pH-ISFET with a-Si:H gate insulator deposited by the PE-LPCVD system in this paper. The thickness of the a-Si:H was about 2000 A. The temperature is controlled by the P.I.D. temperature controlled system and the hysteresis behaviour is measured by the constant voltage-constant current circuit and voltage-time recorder. The measurement is completed at 25 degree(s)C, 35 degree(s)C, 45 degree(s)C and 55 degree(s)C and the time after the pH changed is 4 min, The experimental results also compared with other materials of the gate insulator for pH-ISFET at the room temperature.
In the past years, the aluminum nitride (AIN) thin films were usually applied to the surface acoustic wave (SAW) devices, optical devices in the ultraviolet spectral region, acousto-optic devices and integrated circuit packaging. In this study, we first selected the AIN thin film as gate insulator for pH sensing ISFET in our laboratory. We have studied the relationship between pH sensitivity and surface potential for AIN gate ISFET in the different solutions. And we also have obtained the pH characteristics from the capacitance-voltage (C-V) and current voltage (I-V) curves. Herein, we can obtain the shift of the linear region threshold voltage of the AIN/SiO2 gate ISFET devices in the different buffer solutions. The AIN materials exhibited a high response, and the sensitivity was about 45~51 mV/pH. In addition, we have also compared with different sensing materials.
KEYWORDS: Field effect transistors, Manufacturing, Temperature metrology, Time metrology, Ions, Electrodes, Silicon, Semiconductors, Digital electronics, Measurement devices
In this study, the commercial manufacture Beckman 110 (Si3N4 gate pH-ISFET) was acted as the sensitive membrane of pH-ISFET. The experimental results show that the Si3N4 material has a fairly high response, and the pH sensitivity was obtained at 56.94 mV/pH in a concentration rage between pH 1 and pH 11 at room temperature. In our experiment, we use Keithley 236 Semiconductor Parameter Analyzer to measure the drain current (IDS) versus gate voltage (VG) curve of Si3N4 ISFET over a pH range from 1 to 11 at room temperature. The constant voltage-current-circuit and time-voltage record were also used to measure the hysteresis curve of Beckman 110 (Si3N4 gate pH-ISFET). The same procedure was also applied to a-Si:H gate pH-ISFET, which fabricated in our laboratory. From the IDS versus VG and hysteresis curve, we can obtain that the pH sensitivity was 56.94 mV/pH at constant temperature (25 degree(s)C) and hysteresis widths of Beckman 110 (Si3N4 gate pH-ISFET) and a- Si:H gate pH-ISFET in the larger pH site are larger than in the smaller pH site, and the hysteresis width increased with the increasing loop time and measureing path.
In this study, we utilize the commercial device, Sentron 1090 Al2O3 gate pH-ISFET to study the sensitivity and hysteresis behaviour. The experimental results show that the Al2O3 materials have a fairly high response, and the sensitivity was obtained from the pH response of Sentron 1090. The hysteresis effect in a Sentron 1090 Al2O3 gate pH-ISFET was studied by exposing the device to two cycles of pH values. The hysteresis curves were measured in the sequence pH 8-3-8-11-8 and pH 7-3-7-11-7 at different loop time. According to experimental results, the hysteresis width is increasing with loop time and measuring path. We also observed and compared the pH sensitivity and magnitude of the hysteresis width with others pH-sensing gate ISFETs studied in our laboratory and the related literatures.
A new highly sensitive photoreceptor in visible-spectrum region with high contrast voltage ratio has been developed for an electrophotographic device. The multilayered amorphous silicon photoreceptor has been prepared with PE- LPCVD and sputtering system. The structure of the photoreceptor consists of four part: (a) Al substrate, (b) a-WO3 blocking layer, (c) a-Si:H(i) photogeneration and transport layer, (d) a-C:H surface protecting layer. In this study, the photoreceptor is exposed with different wavelength and illumination. Keithley 236 Semiconductor Parameter Analyzer is used to measure the current-voltage curves of photoreceptor. In addition, Electrostatic Parameter Analyzer is used to measure the photo-induced discharge curves, which is used to simulate the processes of copying machines. According to the I-V curves and PID curves, we can investigate the transport of photocarrier in photoreceptor and the optoelectronic parameters.
In the research, we simulated the temperature characteristics of the a-Ta2O5 ISFET by the Gouy- Chapman-Stern theory. The values of the pKa and pKb would be induced to calculate the temperature coefficients of the a-Ta2O5 ISFETs for predicting the behaviors of the a-Ta2O5 ISFET under different temperatures. In the experiment we used the method finding the VGS values of the experimental curves by fixed IDS value to get the pH sensitivities at different temperatures. By using the same way we could change the temperatures to find the temperature coefficients in different pH solutions. The relationship of the pH sensitivities of a-Ta2O5 ISFET versus the temperatures were the linear. Oppositely the curves of the temperature coefficients is not linearly obviously.
Because of the pH sensitivity is one of the important characteristic parameters of ISFET devices. The response of ISFET is mainly determined with the type of the sensing membrane, therefore the sensing material plays a significant role. In addition, the hysteresis is the non-ideal and unstable factor of ISFET devices for measuring. Hence, in this study, the pH sensitivity and hysteresis of a-WO3 gate ISFET are investigated, and compare with different sensing membranes.
The ion-sensitive field-effect transistors (IFSETs) with hydrogenated amorphous silicon were fabricated. In this paper, the hydrogenated amorphous silicon acting as sensing membrane was used to investigate the pH response of a-Si:H ISFET. The IDS-VG curves were carried out by I-V measuring system. The basic parameter of a-Si:H ISFET, namely sensitivity was obtained from IDS-VG curves. It exhibited a superior pH response of 50.6 mV/pH at temperature of 25 degrees C. Moreover, other characteristic parameters such as hysteresis and drift were proposed. Finally, the effects of operating temperature on sensitivity and drift were presented.
In our research, the glass was used as a substrate for H+ ion sensitive field effect transistor (ISFET). The sensitive characteristics of five structures for separative extend gate ion sensitive field effect transistors were studied, which include tin oxide/aluminum/micro slide glass, tin oxide/aluminum/corning glass, indium tin oxide (ITO) glass, tin oxide/indium, indium tin oxide glass and tin oxide/micro slide glass. Indium tin oxide thin film is the first time used as a H+ ion sensitive film which has a linear pH sensitivity of Nerstern response, about 58 mV/pH, between pH2 and pH12. In addition, the sensing area effect of the tin oxide/glass, tin oxide/ITO glass and ITO glass structure which without Al conductive layer will be discussed.
In this paper, a high performance CMOS readout structure is proposed and applied for surface micromachined bolometer arrays. The silicon readout circuit is an important interface circuit for detector array and signal processing stages in the IR image syste. Conventional readout configurations for thermal resistive sensors can be classified into four groups (1) Constant Temperature (CT), (2) Constant Current (CC), (3) Constant Voltage (CV), (4) Constant Bias (CB). To achieve a high performance readout and fit the working characteristics of IR detector material, new CMOS readout structures have been developed and fabricated. Based on the application of the proposed CC input biasing technique, a new CMOS Bandgap Reference Constant Current readout structure is proposed and analyzed. The low power CMOS readout circuit is achieved using the reset switch techniques. By applying the proposed bias technique to improve low power, high linearity and low sensitivity of the resistive bolometer detectors and high performance readout interface circuit for the IR linear array is realized with a pixel size of 50 X 50 micrometers 2.
Based on the application of the direct injection for per detector (DI) input technique, a new readout structure for the infrared (IR) focal-plane-array (FPA), called the variable gain direct inject per detector (VGDI) is proposed and analyzed. The readout circuit of VGDI of a unit cell of photo- voltaic sensor under investigation, is composed of a direct inject per detector circuit, high gain amplifier, and the reset switch. The VGDI readout chip has been designed in 0.5 micrometer double-poly-double-metal (DPDM) n-well CMOS technology in various formats from 8 X 8 to 128 X 128. The simulation 8 X 8 VGDI of the readout chip have successfully verified both the readout function and performance. The high gain, low power, high sensitivity readout performances are achieved in a 50 X 50 micrometer2 pixel size.
Based on the application of the source follower per detector (SFD) input biasing technique, a new redout structure for the IR focal-plane-array (FPA), called the variable gain source follower per detector (VGSFD) is proposed and analyzed. The readout circuit of VGSFD of a unit cell of pyroelectric sensor under investigation, is composed of a source follower per detector circuit, high gain amplifier, and the reset switch. The VGSFD readout chip has been designed in 0.5 micrometers double-poly-double-metal n-well CMOS technology in various formats from 8 by 8 to 128 by 128. The experimental 8 by 8 VGSFD measurement results of the fabricated readout chip at room temperature have successfully verified both the readout function and performance. The high gain, low power, high sensitivity readout performances are achieved in a 50 by 50 micrometers 2 pixel size.
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