Masaru Takabatake

CMOS circuits for peripheral circuit integrated poly-Si TFT LCD fabricated at low temperature below 600 degrees C

CMOS shift registers, buffers, and gray-scale representation circuits for integrated peripheral drive circuits of poly-Si TFT LCDs were fabricated at temperatures below 600 degrees C on a glass substrate. The maximum operation frequency of the CMOS shift register was 1.25 MHz. The total power consumption of the 10 stage CMOS shift registers at a clock frequency of 46.8 kHz and a power supply voltage of 20 V was 10 mu W, which is three orders of magnitude smaller than that of 10-stage nMOS shift registers. The rise and fall times of the CMOS buffers were proportional to the inverse of the channel width, and the write time of the gray-scale representation circuits was proportional to the line memory capacitance. >

Structural Change during Annealing of Amorphous Indium-Tin Oxide Films Deposited by Sputtering with H2O Addition

This paper describes the effects of annealing on electric properties and structure of amorphous indium-tin oxide (ITO) films deposited by sputtering at room temperature and with H2O addition. The film resistivity was increased by annealing at 150–200° C; in this temperature range the growth of ITO crystallites dispersed in the amorphous ITO phase was observed. This increased resistivity was found to be due to decreases in both Hall mobility (µ H) and carrier density (n) of the films. Measurements of thermal desorption spectroscopy revealed that two different adsorption states, in terms of H2O molecules which are due to the hydrogen-bonded H2O and OH species, were formed in amorphous ITO films during film deposition and the subsequent annealing process. Factors in the decreases of µ H and n were discussed on the basis of the experimental results obtained.

Indium Tin Oxide Dry Etching Using HBr Gas for Thin‐Film Transistor Liquid Crystal Displays

The dry etching technique for indium tin oxide (ITO) films has been investigated using HBr gas with a conventional parallel-plate-type reactive ion etching apparatus in order to fabricate ITO fine patterns for thin-film transistor addressed liquid crystal displays (TFT-LCDS). Etching rates of amorphous ITO and poly-ITO were almost the same, unlike the case with ITO wet etching. This demonstrates that the ITO etching rate using HBr gas is independent of the film characteristics. A scanning electron microscopy study of etched ITO films showed that the reaction products were not deposited on the sample surface, although the resist surface was roughened. Al films, which are the underlayers of ITO films for TFT-LCDs, were not etched by HBr gas only. Therefore, high ITO/Al selectivity can be obtained by HBr gas.

Roles of bonded hydrogens and oxygen vacancies on crystallization of hydrogenated amorphous indium tin oxide (a-ITO:H) films

Abstract Hydrogenated amorphous indium-tin oxide (a-ITO:H) films were made by sputtering at room temperature with H2O partial pressure as a parameter and initial stage of the thermal crystallization was investigated after 1 h annealing at 150°C. The volume fraction of the nanometer sized crystallites embedded in the amorphous host was minimized at a certain H2O pressure. For lower and higher H2O pressure, the causes of the increase in the crystallites after annealing were different: for lower H2O pressure it was due to the increase in size of the crystallites, whereas for higher H2O pressure it was due to the increase in number of the crystallites. The roles of bonded hydrogens and the oxygen vacancies, which increased and decreased with H2O pressure respectively, are discussed considering the kinetic model for nucleation and growth of crystalline particles in amorphous media.

Vertical-Type Amorphous-Silicon Field-Effect Transistors with Small Parasitic Elements

1 µm-long vertical-type amorphous-silicon field-effect transistors with small parasitic elements have been fabricated and evaluated. Field-effect mobility, mutual conductance and input capacitance per unit channel width were 0.1 cm2/Vs,10 µS/mm and 0.55 pF/mm, respectively. Cut-off frequency evaluated from these values was 3 MHz.

Consideration of feed-through voltage in amorphous-Si TFT's

Feedthrough voltage is an important factor in designing integrated data drive circuits and display area in thin-film-transistor liquid-crystal displays (TFT LCDs). With respect to feedthrough voltage, only the gate-source overlay capacitance has been considered in amorphous-Si (a-Si) TFTs, because of their staggered structure with overlap area. It is pointed out that, in a-Si TFTs designed as active elements, feedthrough voltage is mainly due to the carrier redistribution. The main reason is that, since the field-effect mobility is low (W/L>1), the leakage current must be kept low (L>or=10 mu m), and an active layer is inserted in the overlap area (unlike the case with MOS device structures), the area of the active layer is large. Taking the carrier redistribution into account, the maximum difference between the voltage obtained using the modified model and the experimental voltage is within 20%. By comparison, the results obtained using the previous model for TFTs are approximately three times smaller than the experimental results. >

Low Resistivity Transparent Indium Tin Oxide (Ito) Films Sputtered At Room Temperature With H 2 O Addition

A new kind of amorphous indium tin oxide (ITO) film with good pattern delineation properties and mass production capability, as well as low resistivity and high transparency has been developed. The film was prepared by a cluster-type DC magnetron sputtering apparatus at room temperature with H 2 O addition to the argon sputtering gas. The amorphous ITO film quality was improved by effective termination of oxygen vacancies with -OH species generated by enhanced decomposition from the added H 2 O in the plasma.