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  • The Electrochemical Society  (12)
  • 2015-2019  (12)
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  • The Electrochemical Society  (12)
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  • 2015-2019  (12)
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  • 1
    Online Resource
    Online Resource
    The Oxide TFT By Anodic Oxidation
    The Electrochemical Society ; 2016
    In:  ECS Meeting Abstracts Vol. MA2016-02, No. 33 ( 2016-09-01), p. 2165-2165
    Details
    In: ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2016-02, No. 33 ( 2016-09-01), p. 2165-2165
    Abstract: Oxide-TFTs (thin film transistors) have been studied and are being applied to the AMLCD and AMOLED. One advantage of the oxide TFT is higher mobility than amorphous silicon TFT. The oxide material such as IGZO (indium gallium zinc oxide) is sputtered for the active layer. In this experiment, we used anodic oxide instead of sputtered oxide layer. Anodizing is to oxidize the metal by applying the positive voltage to the metal in the electrolyte. Al and Ti metals were anodized and the anodization is possible even at room temperature. There are two ways of the anodization, one is the barrier type and the other is the porous type. For the electrical device application, a barrier type anodic oxidation is necessary. In the case of Al, thickness of the barrier type anodic oxide is proportional to the anodizing voltage in the electrolyte of citric acid. The oxidation starts at a constant current mode and changes to the constant voltage mode. The anodic oxide of Al was used for the gate insulator of the oxide TFTs. On a glass substrate, gate electrode was patterned after deposition of Al by DC-Sputtering. The Al was anodized to form an Aluminum oxide for the gate insulator. After deposition of Ti, it was patterned for the source/drain electrodes and an active region. After coating photoresist, it was opened on the region where the metal should be anodized to be an active region. The oxidized region of the Ti becomes the active region of the TFT. After removing the photoresist, it was annealed under the oxygen ambient to improve the TFT characteristics. During the anodization, the adhesion of the photoresist to the metal was deteriorated and the anodic oxidation occurred under the photoresist. To solve the problem, we deposited silicon oxide before coating the photoresist. After developing photoresist for the opening of the photoresist, the wet etching of the silicon oxide was performed, which made it possible to accomplish the anodic oxidation without the adhesion problem.
    Type of Medium: Online Resource
    ISSN: 2151-2043
    URL: Article
    DOI: 10.1149/MA2016-02/33/2165
    Language: Unknown
    Publisher: The Electrochemical Society
    Publication Date: 2016
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  • 2
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    Online Resource
    The Oxide TFT with Solution Based Gate Insulator
    The Electrochemical Society ; 2016
    In:  ECS Meeting Abstracts Vol. MA2016-02, No. 33 ( 2016-09-01), p. 2164-2164
    Details
    In: ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2016-02, No. 33 ( 2016-09-01), p. 2164-2164
    Abstract: Low temperature poly-Silicon (LTPS) thin film transistor (TFT) and Oxide TFT are developed for the better performance of the active matrix display. Recently, oxide TFT has been investigated intensively due to simple process and higher mobility than amorphous silicon TFT. Typical parameters of TFT are mobility, threshold voltage and On/Off ratio which are influenced by gate insulator. The widely used material for gate insulator is SiO 2 which is rich in the earth and inexpensive. But vacuum equipments like the plasma enhanced chemical vapor deposition (PECVD) and the RF Magnetron sputter need large investment and maintenance cost than non-vacuum process. Oxide TFT of top gate structure reduces the parasitic capacitance between source-drain and gate metal. The plasma damage during deposition of gate insulator on an oxide active layer cause the defects which deteriorate TFT characteristics. However, the gate insulator by solution process reduces the defects by plasma process. SU-8 which is a negative photoresist (PR) has been being used widely in micro electro mechanical system (MEMS). It is constituted with octuple epoxy groups and includes photosensitize to react with UV light. The polymer network generated by cross-linking has mechanical and chemical stabilities and high electrical resistance. In this experiments, SU-8 was used for the gate insulator of the oxide TFT and investigated the effect of the SU-8 gate insulator on the oxide TFT. In this paper, we investigated the characteristics of gate insulator of SU-8 as changing UV exposure time to SU-8. SU-8 was coated by spin coating with 2000 rpm on a p-type Si wafer. After soft-bake for 1.5 min at 95˚C, UV of 365 nm was exposed at an energy of 320mJ/s. Exposure times were varied as 30s, 60s, 120s, and 240s. After UV exposure, hard bake was done for 20 min at 115˚C. An Al layer was deposited on SU-8, and electrical properties of the SU-8 were measured after post-annealing. Figure 1 shows the current densities of the SU-8 insulators for various exposure time from 30s to 240s. As shown in Fig. 1, the leakage currents decreased as the exposure time increased from 30s to 240s. For the gate insulator of the oxide TFT, the proper UV exposure is important. Figure 1
    Type of Medium: Online Resource
    ISSN: 2151-2043
    URL: Article
    DOI: 10.1149/MA2016-02/33/2164
    Language: Unknown
    Publisher: The Electrochemical Society
    Publication Date: 2016
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  • 3
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    Online Resource
    Interfacial Reaction between Metal and Oxide
    The Electrochemical Society ; 2018
    In:  ECS Meeting Abstracts Vol. MA2018-02, No. 36 ( 2018-07-23), p. 1232-1232
    Details
    In: ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2018-02, No. 36 ( 2018-07-23), p. 1232-1232
    Abstract: Transparent oxide semiconductor thin film transistor (TFT) is being used in display such as OLED (organic light emitting diode) display and LCD (liquid crystal display). The active oxide layer in oxide TFT is transparent, comprising band gap higher than 3.0 eV. In TFT fabrication metal layer contacts to the active oxide layer and the reaction between active oxide layer and metal degrade TFT characteristics due to thin metal oxide formation. In this paper the reaction between the amorphous indium- gallium -oxide (a-IGZO) and metal was studied. Metal oxide formation was reported with interfacial micro-structures between a-IGZO and the metal electrode. TiO x is formed at the interfacial region between Ti and IGZO layers by oxygen out-diffusion from IGZO. The reaction depends on process parameters such as temperature, annealing time and the environment of annealing. For several metals such as Al, Ti, and Mo, the interfacial reaction by thermal anneal was compared for various annealing conditions. The a-IGZO was deposited on ITO electrode layer and the 0.8 mm diameter metal electrodes are formed on a-IGZO layer. After annealing at various conditions, formation of metal oxide was verified by electrical characteristics. The leakage current and breakdown voltages were measured. Figure 1 shows typical I-V characteristics between metal and ITO electrode. Figure 1
    Type of Medium: Online Resource
    ISSN: 2151-2043
    URL: Article
    DOI: 10.1149/MA2018-02/36/1232
    Language: Unknown
    Publisher: The Electrochemical Society
    Publication Date: 2018
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  • 4
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    Online Resource
    Oxide TFT with Sog Gate Insulator
    The Electrochemical Society ; 2016
    In:  ECS Meeting Abstracts Vol. MA2016-02, No. 33 ( 2016-09-01), p. 2161-2161
    Details
    In: ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2016-02, No. 33 ( 2016-09-01), p. 2161-2161
    Abstract: Oxide TFT (thin film transistor) shows higher mobility and less leakage current than amorphous silicon TFT. In this presentation, we investigated solution processed gate insulator for the oxide TFT. The solution process does not require the use of expensive vacuum equipment, and also has advantages of simple process, high productivity and low cost. Less defects and trap centers are required for the gate insulator and the conventional material is SiO2 for which vacuum equipments are used to deposit it. Since the gate insulator is deposited on the active layer for the top gate structure, active layer can be deteriorated by plasma ion bombardment during deposition of the gate insulator. Plasma damage exerted on the active layer during the deposition of the gate insulator have an adverse effect on the TFT characteristics. On the other hand, solution process does not use plasma, therefore, it can remove plasma damage on the active layer. And also, solution process is inexpensive and highly productive process. In this experiments, we used spin on glass material for the solution process of the gate insulator. We investigated the effect of dilution of the SOG with IPA (isopropyl alcohol). It was coated on a p-type Si wafer by spin coating with 3500 rpm. For the diluted solution, we coated several times for the desired thickness of the gate insulator. Hard bake was done for 20 min at 170℃ after soft-bake for 20 min at 85℃. Final cure was done for 1 hour at 420℃ in nitrogen ambient. Figure 1 shows the current densities of the SOG insulator for the various dilutions of SOG solution. The leakage currents were reduced for the diluted solution. Figure 1
    Type of Medium: Online Resource
    ISSN: 2151-2043
    URL: Article
    DOI: 10.1149/MA2016-02/33/2161
    Language: Unknown
    Publisher: The Electrochemical Society
    Publication Date: 2016
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  • 5
    Online Resource
    Online Resource
    Operational Amplifier Circuits with Oxide Thin Film Transistors
    The Electrochemical Society ; 2016
    In:  ECS Meeting Abstracts Vol. MA2016-02, No. 33 ( 2016-09-01), p. 2166-2166
    Details
    In: ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2016-02, No. 33 ( 2016-09-01), p. 2166-2166
    Abstract: Amorphous silicon thin film transistors (TFTs) have been used widely due to good uniformity and low process cost. However, They are not suitable for a circuit due to the low carrier mobility. Amorphous Indium-Gallium-Zinc-Oxide Thin Film Transistor (a-IGZO TFT) exhibits higher mobility and lower leakage current than amorphous silicon TFT and it is common to use only n-type a-IGZO TFT due to a poor electrical property of p-type TFT. In this paper, we developed operational amplifier (op-amp) circuit using only the n-type a-IGZO TFTs. Recently, medical device circuits for measuring bio-signals are being implemented on a wearable devices. Oxide TFTs are suitable for the integrated circuit for such applications. The analog signal processing such as amplification, and filtering of much noise are necessary for analog electrical signals introduced from bio-sensors. The op-amp is most widely used amplifiers due to ideal linear performance characteristics. An op-amp is composed of two input voltages (+V in , -V in ), two power supply voltages (+V DD , -V DD ) and one output voltage (Vout). It amplifies the voltage difference between the two input voltages of the non-inverting and inverting inputs (+V in , -V in ). The op-amp with a-IGZO TFTs has lower gain than that of the op-amp by CMOS process and need increase of the gain by cascaded amplifier stages. We developed a single power supply (+V DD = +15V) OP amp with improved gain. The circuit is composed of three stages: the first is differential amplifier(T1~T8) of input stage, the second is common-source amplifier(T9~T17), and the third is output buffer(T18~T19) of the output stage. The differential amplifier of the first stage amplified the differential voltage for given input signals (+V in , -V in ). The output voltage was amplified at the common-source amplifier stage of the second stage. Common-source amplifiers were used for a large voltage gain. After optimization of the circuits, the input voltage of 0.05V was amplified to about 13V.
    Type of Medium: Online Resource
    ISSN: 2151-2043
    URL: Article
    DOI: 10.1149/MA2016-02/33/2166
    Language: Unknown
    Publisher: The Electrochemical Society
    Publication Date: 2016
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  • 6
    Online Resource
    Online Resource
    Integrated Taste Sensor Circuit with Oxide TFT
    The Electrochemical Society ; 2018
    In:  ECS Meeting Abstracts Vol. MA2018-02, No. 36 ( 2018-07-23), p. 1226-1226
    Details
    In: ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2018-02, No. 36 ( 2018-07-23), p. 1226-1226
    Abstract: Among the sensors that imitating the human five senses, the visual sensors are commercialized as CIS (CMOS Image Sensor) and CCD (Charge Coupled Device), and tactile sensor are partly commercialized as a touch sensor. Also, auditory sensor is commercialized as a microphone. However, the smell and taste sensors are still under development. If the taste is sensed electrically, it is possible to obtain standard taste information. For portable applications a small size taste sensor system is required and a suitable technology for manufacturing such a highly sensitive small-sized sensor is semiconductor technology. Conventional taste sensors require a large amount of test material because they are large in volume. Also require expensive equipment and not suitable for portable device. Various types of biosensors have been developed to overcome these drawbacks. The FET-type biosensor has advantages of miniaturization and standardization by integrating the sensor and the circuit by utilizing the integrated circuit manufacturing process. Among the devices capable of integrated circuits, thin film transistors with oxide semiconductor materials are one of the candidates having a simpler process than the LTPS TFT and a higher field effect mobility than the a-Si TFT. Depending on the taste substances, the emitter current in the FET sensor changes. Each taste solution and lipid sensing membrane have different sensing principles. For example, a sourness, saltiness, or sweetness solution are electrochemical reactions in which specific ions are assembled near the lipid sensing membrane by electrical attraction, the bitterness solution is hydrophobic and certain molecules are absorbed by the lipid sensing membrane Hydrophobic binding. Those reactions induce potential changes of the floating gate and changes the current of the device. As the concentration of the taste substances increases, the current of the transistor increases. And each solution has different values depending on the lipid sensing membrane. In this paper, an oxide transistor-based amplifier is designed for a taste sensor. We designed an amplifier that works well even when the size of the transistor changes and the threshold voltage changes. Usually amplifier circuit require the optimum operation bias, which make the circuit complicated. However, in this paper we proposed a cascaded Class A amplifier which uses self-bias unit instead of voltage divider by resistors as shown in figure. In this circuit, T3 is a taste sensing transistor. Sensing signal is amplified by supply the alternation voltage through capacitor. The alternative way is to use T4 as a taste sensor. The amplification gains for different location of the sensor were compared. Figure 1
    Type of Medium: Online Resource
    ISSN: 2151-2043
    URL: Article
    DOI: 10.1149/MA2018-02/36/1226
    Language: Unknown
    Publisher: The Electrochemical Society
    Publication Date: 2018
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  • 7
    Online Resource
    Online Resource
    Vertical Channel a-IGZO Thin Film Transistors Using Thin Gate Dielectric
    The Electrochemical Society ; 2018
    In:  ECS Meeting Abstracts Vol. MA2018-02, No. 36 ( 2018-07-23), p. 1231-1231
    Details
    In: ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2018-02, No. 36 ( 2018-07-23), p. 1231-1231
    Abstract: Oxide thin film transistors (TFTs) are widely used as backplane for displays such as active matrix organic light emitting diode display and active matrix liquid crystal display. And also, it can be used in many applications such as sensor and wearable devices which require small power consumption. For low power consumption, the operation voltage should be decreased and the vertical structure TFT is a candidate due to short channel length. In this study, we proposed a vertical structure TFTs using a thin gate dielectric. In this experiment, a vertical structure TFTs with a channel formed on the vertical sidewall of the gate electrode and a channel length controlled by the thickness of the gate electrode is proposed. The channel length was adjusted by the thickness of the gate electrode in the vertical TFTs developed in this paper. Figure 1 shows the fabricated vertical a-IGZO TFT developed in this study. This vertical TFTs has the feature of controlling the channel length by the thickness of the gate electrode and can achieve short channel length easily, which is useful for low driving voltage. To reduce the gate voltage also, the thin gate dielectric was used. Since the very thin gate insulator was used, low threshold voltage was obtained, and low voltage driving was possible. Figure 1
    Type of Medium: Online Resource
    ISSN: 2151-2043
    URL: Article
    DOI: 10.1149/MA2018-02/36/1231
    Language: Unknown
    Publisher: The Electrochemical Society
    Publication Date: 2018
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  • 8
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    Online Resource
    Solution Based Al 2 O 3 Gate Insulator for Low Temperature Poly Silicon TFT
    The Electrochemical Society ; 2018
    In:  ECS Meeting Abstracts Vol. MA2018-02, No. 36 ( 2018-07-23), p. 1228-1228
    Details
    In: ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2018-02, No. 36 ( 2018-07-23), p. 1228-1228
    Abstract: Solution based insulator was applied for low temperature poly silicon thin film transistor (TFT). Solution process has several advantages of low cost, short process time and no plasma damage. Several kinds of solution-based materials were tested for TFTs, including organic insulators. In this paper, we present the aluminum oxide gate insulator based on solution process. For poly-silicon process, amorphous silicon is deposited by sputtering and crystallized by blue laser diode annealing. After pattering of the poly-silicon, gate insulator of Al 2 O 3 was formed by solution process. After gate insulator etching, source/drain metal was deposited and patterned. Low temperature process below 400℃ for all TFT fabrication with low cost has been developed and reported. The insulator was characterized with the metal-insulator-semiconductor (MIS) structure. 0.8 M Al(NO 3 ) 3 9H 2 O solution with DMAC (Di-methyl-acetamide) was coated on the Si-wafer. The surface of silicon wafer was treated with oxygen plasma before coating to improve the adhesion. After spin-coating, it was baked at 150℃ for 5 min. It was annealed finally at 300℃ for 1 h. To improve the insulator performance, the multi coating was tested. After coating and baking, it was coated again. Figure 1 shows the I-V characteristics for the sample coated for three times. As the number of coating increased, leakage current was reduced and the break down voltage increased. Figure 1
    Type of Medium: Online Resource
    ISSN: 2151-2043
    URL: Article
    DOI: 10.1149/MA2018-02/36/1228
    Language: Unknown
    Publisher: The Electrochemical Society
    Publication Date: 2018
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  • 9
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    Online Resource
    Amplifier Circuit with Oxide TFT
    The Electrochemical Society ; 2016
    In:  ECS Meeting Abstracts Vol. MA2016-02, No. 33 ( 2016-09-01), p. 2162-2162
    Details
    In: ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2016-02, No. 33 ( 2016-09-01), p. 2162-2162
    Abstract: Oxide TFT (thin film transistor) has higher electron mobility and less leakage current than amorphous silicon TFT. Among oxide TFTs such as ZnO, InZnO, InGaZnO and so on, the IGZO TFT has being studied by many researchers and being used in the display backplane. In this presentation, an amplifier circuit with oxide TFTs was developed for the higher voltage gain. Most commonly used type of power amplifier is the Class A Amplifier. The Class A amplifier is the most common and simplest form of power amplifier, in which transistor is always biased on-state so that it conducts during one complete cycle of the input signal waveform producing minimum distortion and maximum amplitude to the output. The efficiency of this type of circuit is low and delivers small power outputs. To get high amplification gain, we designed an amplifier circuit based on inverter and optimized the channel width of each TFTs. The circuit developed is a common source amplifier, which is a single transistor amplifier that the input terminal is the gate and the source, output terminal is the drain and the source. In that type of amplifier circuit, the ratio of the widths of load transistor and drive transistor should be optimized for the highest gain. The DC operating voltage for the input gate electrode is also important, and the conventional way to get the operation voltage is using resistor divider, in which we should design the resistor divider according to the characteristics of TFT. In this presentation, we proposed the auto setting operation voltage scheme instead of resistor divider, and obtained the voltage gain of 14.
    Type of Medium: Online Resource
    ISSN: 2151-2043
    URL: Article
    DOI: 10.1149/MA2016-02/33/2162
    Language: Unknown
    Publisher: The Electrochemical Society
    Publication Date: 2016
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  • 10
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    Online Resource
    Oxide TFT Comparator Suitable for Bio Sensor Platform
    The Electrochemical Society ; 2018
    In:  ECS Meeting Abstracts Vol. MA2018-02, No. 36 ( 2018-07-23), p. 1229-1229
    Details
    In: ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2018-02, No. 36 ( 2018-07-23), p. 1229-1229
    Abstract: As the interest in personal health care is increasing, research on Bio-Information Technology (BIT) continues to be as vigorous as ever. Particularly, efforts are being made to develop products using bio-sensors capable of free movement and prompt detection. Therefore, a health care device with SOG (System-on-glass) technology is required due to the advantages of miniaturization, low cost, and simple process. These bio-sensor platforms must be consisting of the fully integrated circuit in order to be in contact with or embedded in the human body. To display the sensing signal, we need analog-to-digital converter (ADC) circuit and 7-segment decoder which can be integrated using n-type amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) on a substrate. These bio-sensor platforms consist of an integrated circuit that converts the analog signal to a digital signal and the 7-segment decoder to show the signal level. TFTs are required to realize the SOG which integrates all devices on substrates like a glass and plastic etc. Oxide semiconductor TFTs such as a-IGZO TFTs show better performance than amorphous silicon TFTs. Owing to their transparency and higher mobility compared to the amorphous silicon TFTs, a-IGZO TFTs have been studied widely. Figure shows 9 comparators for digitizing, 9-to-4bit priority encoder and 7-sement decoder for display. An OP amp-based comparator includes two inputs, one is an analog input (V in ) and the other is a reference voltage (V ref ) generated by a serially connected resistor array. The input signals are compared with the reference voltages by the comparators, which output “0” or “1” according to the analog input level. Then the binary outputs of the comparator are converted to the binary format (A3, A2, A1, and A0) by a digital encoder. The 4bit outputs (A3, A2, A1, and A0) of the ADC are the inputs of the 7-segment decoder. Among the four outputs of ADC, ‘A0’ is the least significant bit and ‘A3’ is the most significant bit. The outputs of 7-segment decoder are labelled as a, b, c, d, e, f, and g which correspond to each segment of 7-segment display. The 4bit binary codes from ADC are converted to input signals (a to g) of a 7-segment display. Those circuits with a-IGZO TFTs can be used in applications such as the fully integrated bio-sensor platform and wearable device which are transparent and flexible. The most complex one in that platform is OP Amp which is comparator to generate binary code and needs high gain to accomplish good performance. The comparator is a circuit that plays an important role in the ADC, and the operation of the ADC is difficult to expect without the correct operation of the operational amplifier. Thus, we proposed OP Amp type comparator with oxide TFT for bio sensor platform. Figure 1
    Type of Medium: Online Resource
    ISSN: 2151-2043
    URL: Article
    DOI: 10.1149/MA2018-02/36/1229
    Language: Unknown
    Publisher: The Electrochemical Society
    Publication Date: 2018
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