Integrated Taste Sensor Circuit with Oxide TFT

Ever evolving advances in oxide semiconductor materials and devices continue to fuel leading edge developments in display technology, and transparent electronics, thanks to new integration processes, enabling large area processing on rigid and flexible substrates. Nanocrystalline oxide semiconductor offer a host of advantages such as low cost and high scalability, in addition to seamless heterogeneous integration with a host of other inorganic and organic materials in view of its low thermal budget in processing which provides integration flexibility. This has spawned a wealth of applications ranging from high frame rate interactive displays with embedded imaging to flexible electronics, where speed and transparency are essential requirements Therefore, transparent electronic systems, which have been once viewed as science fiction, can now become a reality. In semiconductor device applications, interest in oxide semiconductors stem from a number of attributes primarily their ease of processing, and high field effect mobility, resulting in stackable process nature on silicon circuits. In this talk, various semiconductor device applications via nanocrystalline oxide semiconductor materials will be presented.In the first part of our presentation, as seen in Figure 1, we present a photo-transistor embedded in a display pixel, in which gate operation is used to accelerate recovery from photocurrent level to the dark state. We describe the origin of ultra-high quantum efficiencies in photo-sensors based on nanocrystalline oxide hetero-junction thin film transistor (TFT). In order to understand the origin of high photocurrent of a device, we evaluated the influence of a light spot from source to drain side on the photoconductive gain of photosensor array. This work here demonstrates high sensitivity image sensor along with quantitative analysis of the quantum efficiency in the hetero-junction TFT taking into account the optical absorption, electron lifetime, and transit time.The integration of electronically active oxide components onto silicon circuits represents an innovative approach to improving the functionality of novel devices. Like most semiconductor devices, complementary-metal-oxide-semiconductor image sensors (CISs) (see Figure 2) and memory devices have physical limitations when progressively scaled down to extremely small dimensions. In the 2nd part of presentation, we propose a novel hybrid CIS architecture and memory architectures that are based on the combination of nanometer-scale oxide thin-film transistors (TFTs) and a conventional Si device. The results demonstrate how our stacked hybrid device could be the starting point for new device strategies in image sensor architectures. Furthermore, we expect the proposed approach to be applicable to a wide range of micro- and nanoelectronic devices and systems.

An Image sensor is converts an image into a digital signal. Both CCD (charged coupled device) and CMOS (complementary metal oxide semiconductor) image sensor technologies are essential for image capturing. CMOS image sensor is still in their early years, still it's set to develop but CCD has number of advantages over CMOS. CCD will give you a assurance for more compact, high image quality and potentially more efficient camera. Both CCD and CMOS Technologies have explained in this paper and also how images are captured as well as types for both types of image sensors have been descried. Some issues such as performance characteristics for better image quality for photography have been covered.

Low concentration, multi taste detectable taste sensor using the high transconductance of a cascoded gated lateral bipolar junction transistor

Thin-film transistors (TFTs) that utilize oxide semiconductors as channel materials have been widely used in various electronic device applications, such as displays, sensors, and memory devices. Among the oxide semiconductors, transparent amorphous indium-gallium-zinc oxides (a-IGZO) have superior characteristics, namely, high field-effect mobility (~10cm2/Vs), good uniformity, low processing temperatures, optical transparency, and low-cost fabrication processability compared with conventional amorphous/poly-silicon TFTs. However, oxide TFTs including a-IGZO TFTs have bias stress-induced instabilities, which are still critical issues in launching commercial oxide TFT products. These issues can be attributed to the oxygen vacancy-related defects, which are known to act as a major source of electrons and as carrier traps. To suppress such oxygen vacancy-related defects, many researchers reported various techniques, such as ozone treatment, oxygen annealing on oxide TFTs, passivation, and metal-doped oxide semiconductors.In this study, we investigated the device performance of tantalum (Ta)-doped IGZO TFTs as a function of Ta content. Ta was used as a dopant because of its bond-dissociation-energy (BDE, 805kJ/mol) with oxygen higher than those of In, Ga, and Zn. The Ta-doped IGZO, which was adopted as a channel layer of bottom-gate TFTs, was fabricated using a magnetron co-sputtering method. Heavily doped p-type Si wafer with thermally grown SiO2 (300nm) was used as substrates. The RF power for the a-IGZO (In2O3 :Ga2O3 : ZnO = 1:1:1)target was fixed at 100 W while the power for the Ta target increased from 0 to 50 W. Aluminum (Al) was deposited as source/drain electrodes using an electron beam evaporator. With increasing Ta content in the IGZO films, the field-effect mobility (μFE) of the Ta-doped IGZO TFTs decreased, the threshold voltage (Vth) increased from negative to positive values, and the subthreshold swing (SS) became smaller with higher on/off ratio. Especially, Ta (10W)-doped IGZO TFTs exhibited μFE of 7.11 cm2/Vs, a SS of 0.195V/decade, and an on/off ratio ~1x108. These results show that the Ta-doping improves the switching characteristics of the Ta-IGZO TFTs. Furthermore, to evaluate the bias-stress stability, positive bias stress (PBS), negative bias stress (NBS) tests were conducted.

High-performance solid-phase crystallized (SPC) polycrystalline silicon thin-film transistors (TFTs) with argon ion implantation (argon-implanted poly- TFTs) are proposed in this study. Compared to the control poly- TFT, the argon-implanted poly- TFT has superior electrical characteristics, including lower threshold voltage, higher field-effect mobility, steeper subthreshold swing, lower trap state density, etc. These electrical performance improvements could be attributed to the fine microstructure of the SPC poly- film improved by deep argon ion implantation beyond the interface of amorphous and underlying oxide. Therefore, a high-quality poly- channel accompanied with larger grain size and lower grain boundary trap states could be obtained. Moreover, the argon-implanted poly- TFT also exhibits an improved hot-carrier stress immunity owing to reduced weak or bonds from fewer grain boundaries in the poly- channel.

Transparent thin film transistors (TFTs) have been the subject of extensive scientific research over the last couple of decades, for applications in displays and imaging, as their implementation in active-matrix liquid crystal displays backplanes is expected to improve their performance in terms of switching times and stability. To this end, several material systems have emerged as contenders to address this need for a high performance, low power, large-area electronics i.e. thin film silicon, organic semiconductors and metal oxides. The electronic limitations of thin film silicon are well documented, and although organic semiconductors have seen significant improvements in recent years, their persistent low mobility and instability means that they are unlikely to progress beyond niche applications. This thesis is focused on the investigation of the physical properties of metal oxides and their implementation in TFTs. Metal oxide based TFTs were fabricated by spray pyrolysis, a simple and large-area-compatible deposition technique. More precisely, the implementation of titanium-aluminate and niobium-aluminate both wide band gap and high-k gate dielectric metal oxides in solution processed ZnO-based TFTs was studied and high performance, low operational voltage devices were fabricated. ZnO-based TFTs employing stoichiometric Al2O3-TiO2 (k~13, Eg~4.5 eV) or Nb2O5-Al2O3 (k~13.5, Eg~5.1 eV) as gate dielectric exhibited low leakage currents, high on-off current modulation ratios, high field-effect mobilities and low subthreshold voltage swings. Furthermore, the implementation of solution-processed crystalline indium-zinc oxide (c-IZO) as active channel material in TFTs was equally investigated and high-performance c-IZO-based TFTs employing Al2O3 were fabricated. The effects of metal cation doping in c-IZO matrix were investigated in particular, and c-IZO:X (X:Ga,Y,Zr,Nb) based TFTs were fabricated and their properties were assessed for each dopant. Amongst them, Yttrium doped c-IZO (c-YIZO)-based TFTs exhibited the best performance in terms of low off-state currents, high field-effect mobilities and low subthreshold voltage swings.

We studied a-Si:H thin film transistors (TFTs) with gate metal/substrate combinations, including Cr or Al/Cr gate metal on plain Kapton, and Cr/Al/Cr on SiN x passivated Kapton, to identify effects of roughness on TFT performance. TFTs with Cr/Al/Cr on SiN x passivated Kapton are superior in the essential characteristics: low threshold voltage, low gate leakage current I gs , high on-current, high field-effect mobility, and steep subthreshold slope. The off-current is comparable to those of TFTs on plain Kapton. The Igs of all TFTs rises with increasing surface roughness of the gate metal. The major contributor to roughness is the metal film itself, not the substrate.

Today, CCD and CMOS image sensors have found many applications in general public domains. However their use for scientific and space applications requires high electro optical performances and strong abilities to predict them prior to the image sensors design and conception. Sensitivity and image quality are two important electro-optical characteristics for an image sensor. The Quantum Efficiency (QE) and the Modulation Transfer Function (MTF) are respectively the common metrics used to quantify them. Because of an important number of parameters influencing the MTF and the QE, their analytical calculation is not an easy task. This paper describes an analytical model of MTF and QE of CCD and CMOS image sensors. The model has been developed in order to take into account a maximum number of parameters: pixel size, photosensitive area size and shape, EPI-layer and substrate doping concentration, junction depth. The effect of top layer oxide stacks on the resulting optical transmission coefficient and so on QE can also be taken into account. The study is established in the case of CMOS photodiode pixels and buried channel CCD pixels. The MTF and QE modeling results are compared with experimental results. MTF and QE measurements are realized on different pixels types having different photosensitive area shapes and using different technologies. A part of these measurements are performed on a frontside-illuminated CMOS sensor and on a thinned backside-illuminated CMOS image sensor, both of them are manufactured using CMOS technology dedicated to image sensors. The other part of MTF and QE measurements are performed on thinned backside-illuminated N-buried channel CCD sensor. Finally the MTF and QE models are used to make performance predictions, and the effects of various parameters on the MTF and the QE are discussed.

Since the birth of charge coupled devices (CCD) and the complementary metal-oxide-semiconductor (CMOS) active pixel sensors, pixel pitch of digital image sensors has been continuously shrinking to meet the resolution and size requirements of the cameras. However, shrinking pixels reduces the maximum number of photons a sensor can hold, a phenomenon broadly known as the full-well capacity limit. The drop in full-well capacity causes drop in signal-to-noise ratio and dynamic range.The Quanta Image Sensor (QIS) is a class of solid-state image sensors proposed by Eric Fossum in 2005 as a potential solution for the limited full-well capacity problem. QIS is envisioned to be the next generation image sensor after CCD and CMOS since it enables sub-diffraction-limit pixels without the inherited problems of pixel shrinking. Equipped with a massive number of detectors that have single-photon sensitivity, the sensor counts the incoming photons and triggers a binary response “1” if the photon count exceeds a threshold, or “0” otherwise. To acquire an image, the sensor oversamples the space and time to generate a sequence of binary bit maps. Because of this binary sensing mechanism, the full-well capacity, signal-to-noise ratio and the dynamic range can all be improved using an appropriate image reconstruction algorithm. The contribution of this thesis is to address three image processing problems in QIS: 1) Image reconstruction, 2) Threshold design and 3) Color filter array design.Part 1 of the thesis focuses on reconstructing the latent grayscale image from the QIS binary measurements. Image reconstruction is a necessary step for QIS because the raw binary measurements are not images. Previous methods in the literature use iterative algorithms which are computationally expensive. By modeling the QIS binary measurements as quantized Poisson random variables, a new non-iterative image reconstruction method based on the Transform-Denoise framework is proposed. Experimental results show that the new method produces better quality images while requiring less computing time.Part 2 of the thesis considers the threshold design problem of a QIS. A spatially-varying threshold can significantly improve the reconstruction quality and the dynamic range. However, no known method of how to achieve this can be found in the literature. The theoretical analysis of this part shows that the optimal threshold should match with the underlying pixel intensity. In addition, the analysis proves the existence of a set of thresholds around the optimal threshold that give asymptotically unbiased reconstructions. The asymptotic unbiasedness has a phase transition behavior. A new threshold update scheme based on this idea is proposed. Experimentally, the new method can provide good estimates of the thresholds with less computing budget compared to existing methods.Part 3 of the thesis extends QIS capabilities to color imaging by studying how a color filter array should be designed. Because of the small pixel pitch of QIS, crosstalk between neighboring pixels is inevitable and should be considered when designing the color filter arrays. However, optimizing the light efficiency while suppressing aliasing and crosstalk in a color filter array are conflicting tasks. A new optimization framework is proposed to solve the problem. The new framework unifies several mainstream design criteria while offering generality and flexibility. Extensive experimental comparisons demonstrate the effectiveness of the framework.

We report the effect of repeated tensile bending stress on the electrical performance of amorphous-indium–gallium–zinc-oxide (a-IGZO) thin-film transis- tors (TFTs) with source/drain offset. The tensile strain induces the negative transfer shift for the conventional TFTs, but the ON-current ( ${I}_{ \mathrm{\scriptscriptstyle ON}}$ ) increases significantly for the offset TFTs with negligible change in threshold voltage ( ${V}_{\textsf {TH}}$ ). The experimental results can be fitted well with technology computer aided design simulation by the generation of donor-like states in the bending region of the a-IGZO semiconductor. The degraded TFT performance can be completely recovered by thermal annealing at 250 °C for 1 h, confirming the generation of the donor-like metastable defects, oxygen vacancies.

The purpose of this study is to reproduce tastes expect the five basic tastes with a multichannel taste sensor. The sensor can isolate and detect five tastes. The basic taste evaluation is expressed in terms of the concentration of typical tasting substances. For example, if the taste is salty, the sensor output for sodium chloride is obtained data and converted to an equivalent sodium chloride concentration from the sensor output of the unknown taste solution. In the case of rice taste, we found it difficult to describe it in terms of a combination of the five basic tastes. In the existing sensory test of rice, there are no items defined that correspond to taste in the narrow sense. We estimated that rice tastes other than the five basic tastes. Therefore, we first analyzed to find out what the taste substances were in the rice. The response characteristics of a multichannel taste sensor for rice were determined. The inorganic ionic components in rice were analyzed, and a mixed solution containing the obtained taste substances, NaH2PO4 and CaCl2, was prepared, and it was shown to have the same sensor output as that of the rice extract. The results of this study suggest that as the mixture is made from two substances, a quantitative evaluation of rice taste can be made on two axes: the taste sensor output corresponding to the concentration of each substance.

The elaboration of a sensitive taste sensor for discrimination of different soft drinks is very important in food industry. The short review of taste sensors described in the literature is presented. Two types of potentiometric taste sensors, one with lipophilic compound-polymer membranes (ISE) and the other with lipid polymer membrane and a conducting polymer film (All solid state electrode, ASSE) were tested in appropriate taste solutions. Five channel ISE sensor was examined in acid, sour and sweet solutions. This sensor was sensitive to bitter and sour substances and not too sensitive to sucrose concentration. It was successfully used for discrimination of different kind of soft drinks. Four channel ASSE sensor was examined in sour solutions. It was found that stability and sensitivity of ASSE are lower than ISE. Therefore, it seems that the previous one cannot be applied in taste sensor.

Heterogeneous monolithic 3D integration for hybrid vertical CMOS inverter using n-type IGTO TFT on p-type Si FET

Direct and indirect imaging detectors for digital radiography have been developed during the past a few years. Among scintillators, columnar CsI(Tl) screens are used for indirect digital X-ray imaging for industrial and medical radiography. By the help of recent developments CMOS (Complementary Metal Oxide Semiconductor) is replacing the CCD (Charge Coupled Devices) in X-ray image sensor because of low operating power, standard CMOS manufacturing process, and low cost. An X-ray imaging detector consisting of pixelated CsI(Tl) scintillator and CMOS imaging sensor for application in dental radiography was developed. The manufactured CMOS imaging sensor has 128 by 128 pixels with the pitch size of 50 mum and gap width of 5 mum. A 0.5 mum CMOS process was used for sensor fabrication. Pixel structured CsI(Tl) scintillator was directly deposited on the patterned CMOS imaging sensor by thermal evaporation and photo-lithography process. The fabricated monolithic X-ray imaging sensor showed dramatic improvement in spatial resolution due to enhancement of the scintillation light guiding effect and reduction of the light cross-talk between scintillator pixels.

There are reports of fabrication of taste sensor by adsorbing lipids into Millipore filter paper. With this lipid based sensor, it has been found that the taste sensing efficiency of membrane can be remarkably improved. We have made an attempt to prepare taste sensor material by using functionalized polymer without any lipid. PVA-cellulose composite has been modified to use as the sensor material. The research work covers polymer membrane preparation, morphology study and structural characterization of the membrane and study of the taste sensing characteristics of this membrane for five different taste substances. PVA-cellulose composite membrane was modified by phosphorylation with POCl3. FTIR spectroscopic analysis, XRD analysis and SEM were done to get an idea about the structure and morphology of the prepared phosphorylated PVA-cellulose composite membrane. The sensor characteristics like temporal stability, response stability, response to different taste substances, and reproducibility of sensing performance were studied using phosphorylated PVA-cellulose composite membrane. Sensor device prepared with this membrane has shown distinct response patterns for different taste substances in terms of membrane potential. Threshold concentrations of phosphorylated PVA-cellulose composite membrane for HCl, NaCl, Q-HCl, sucrose and MSG are 0001 mM, 0.001 mM, 0.001 mM, 0.001 mM and 0.009 mM, respectively. The threshold concentrations are below human threshold concentrations. Membranes also showed characteristic response patterns for organic acids like acetic acid, citric acid, formic acid etc, mineral acids like HCl, H2SO4 and HNO3 salts, bitter substances, sweet substances and umami substances. Sensor device prepared with this membrane has excellent shelf life.