Sung Min Yoon

42.3: Transparent ZnO Thin Film Transistor for the Application of High Aperture Ratio Bottom Emission AM-OLED Display

We have fabricated 2.5″ QCIF+ bottom emission AM-OLED with aperture ratio of 59.6% using fully transparent ZnO-TFT array and highly conductive oxide/metal/oxide electrode for the first time. The bias stability of ZnO TFT was improved by optimizing ZnO deposition and first gate insulator process. Plasma free process for the gate insulator makes ZnO TFT very stable under electrical bias stress. The Vth shift was less than 0.3V after VDS=25 V and VGS=15 V application for 60 hours. Transparent ZnO TFT characteristics did not change noticeably under irradiation of visible light.

Transparent Al–Zn–Sn–O thin film transistors prepared at low temperature

We have fabricated transparent bottom gate thin film transistors (TFTs) using Al-doped zinc tin oxide (AZTO) as active layers. The AZTO active layer was deposited by rf magnetron sputtering at room temperature. The AZTO TFT showed good TFT performance without postannealing. The field effect mobility and the subthreshold swing were improved by postannealing below 180u2009°C. The AZTO TFT exhibited a field effect mobility (μFET) of 10.1u2002cm2/Vu2009s, a turn-on voltage (Von) of 0.4 V, a subthreshold swing (S/S) of 0.6 V/decade, and an on/off ratio (Ion/Ioff) of 109.

Effect of the electrode materials on the drain-bias stress instabilities of In-Ga-Zn-O thin-film transistors.

The effects of electrode materials on the device stabilities of In-Ga-Zn-O (IGZO) thin-film transistors (TFTs) were investigated under gate- and/or drain-bias stress conditions. The fabricated IGZO TFTs with a top-gate bottom-contact structure exhibited very similar transfer characteristics between the devices using indium-tin oxide (ITO) and titanium electrodes. Typical values of the mobility and threshold voltage of each device were obtained as 13.4 cm(2) V(-1) s(-1) and 0.72 V (ITO device) and 13.8 cm(2) V(-1) s(-1) and 0.66 V (titanium device). Even though the stabilities examined under negative and positive gate-bias stresses showed no degradation for both devices, the instabilities caused by the drain-bias stress were significantly dependent on the types of electrode materials. The negative shifts of the threshold voltage for the ITO and titanium devices after the 10(4)-s-long drain-bias stress were estimated as 2.06 and 0.96 V, respectively. Superior characteristics of the device using titanium electrodes after a higher temperature annealing process were suggested to originate from the formation of a self-limiting barrier layer at interfaces by nanoscale observations using transmission electron microscopy.

Writing current reduction in phase change memory device with U-shaped heater (PCM-U)

For the writing current reduction, we firstly proposed and successfully manufactured phase change memory device with U-shaped heater (PCM-U) device, in which TiN heater surrounds Ge2Sb2Te5 (GST). The experimental results clearly indicate that PCM-U has noticeably shorter SET operation time and 50% smaller RESET current, compared with the conventional. We suggest that the improved properties of PCM-U are due to the overlap of programmable volume.

Transparent Oxide Thin-Film Transistors Composed of Al and Sn -doped Zinc Indium Oxide

We have fabricated the transparent bottom gate thin-film transistors (TFTs) using Al and Sn-doped zinc indium oxide (AT-ZIO) as an active layer. The AT-ZIO active layer was deposited by RF magnetron sputtering at room temperature, and the AT-ZIO TFT showed a field effect mobility of 15.6 cm²/Vs even before annealing. The mobility increased with increasing the In₂O₃ content and postannealing temperature up to 250^degC. The AT-ZIO TFT exhibited a field effect mobility of 30.2 cm²/Vs, a subthreshold swing of 0.17 V/dec, and an on/off current ratio of more than 10⁹ .

Effect of In-Ga-Zn-O active layer channel composition on process temperature for flexible oxide thin-film transistors

In-Ga-Zn-O (IGZO)-channel oxide thin-film transistors (TFTs) were fabricated on flexible polyethylene naphthalate (PEN) substrates. A lamination and delamination procedure was established that allowed easy handling of the PEN substrate during fabrication. In order to fabricate high-performance flexible IGZO TFTs at lower than normal process temperatures, a 2:1:2 (In:Ga:Zn) IGZO channel composition was proposed. The field-effect mobility, threshold voltage, and subthreshold swing of the fabricated IGZO TFTs were found to be approximately 7.83 cm2 V−1 s−1, 1.93u2009V, and 0.24u2009V/decade, respectively, even when a final heat treatment was conducted at a temperature as low as 150u2009u2009°C. The stability characteristics of the devices were also examined under gate bias stress and constant current stress conditions.

Nonvolatile Charge-Trap Memory Transistors With Top-Gate Structure Using In–Ga–Zn-O Active Channel and ZnO Charge-Trap Layer

We proposed a charge-trap-type memory transistor with a top-gate structure composed of Al₂O₃ blocking/ZnO charge-trap/IGZO active/ Al₂O₃ tunneling layer. The memory ON/OFF ratio higher than six-orders-of magnitude was obtained after the programming when the width and amplitude of program pulses were 100 ms and ±20 V, respectively. Excellent endurance was successfully confirmed under the repetitive programming with 10⁴ cycles. The memory ON/OFF ratio higher than 10³ was guaranteed even after the lapse of 10⁴ s. Interestingly, the retention properties were affected by the bias conditions for read-out operations.

Effect of photoenhanced minority carriers in metal-oxide-semiconductor capacitor studied by scanning capacitance microscopy

A scanning capacitance microscope was used to study the photoenhanced minority-carrier contribution to the capacitance of the metal-oxide-semiconductor (MOS) capacitor at high frequencies. When a light is induced over the semiconductor surface, electron-hole pairs are generated and recombined. This steady-state generation-recombination process yields the temporary source of minority carriers, and the inversion layer underneath the oxide layer can respond to very fast-varying ac bias. We measured the differential capacitance (dC/dV) of the MOS capacitor under various light intensities, and observed a peak at the inversion region where the amplitude increased as the irradiation intensity increased. By integrating dC/dV with respect to V, we obtained C–V curves in which the capacitance of the depletion region recovered its value up to that of the accumulation region as the light intensity increased. We also observed that the C–V curves shifted in one direction under irradiation which we believe is due to the...

21.1: Invited Paper: Effect of Channel/Insulator Interface Formation Process on the Oxide TFT Performance

Since the first demonstration of oxide TFT driving AM-OLED, oxide TFT technology has attracted explosive interesting and has been developed for the mass production. The performance of oxide TFT has been verified and the remained issue is bias temperature stability. In this paper, we report the effect of interface process including channel and back channel on the oxide TFT performance in a top gate and a bottom gate structure. We also demonstrate transparent AM-OLED driven by highly stable Al doped ZTO TFT.

Effect of hydrogen in the gate insulator on the bottom gate oxide TFT

Abstract The effect of hydrogen in the alumina gate insulator on the bottom gate oxide thin film transistor (TFT) with an InGaZnO film as the active layer was investigated. TFT with more H‐containing alumina films (TFT A) fabricated via atomic layer deposition using a water precursor showed higher stability under positive and negative bias stresses than that with less H‐containing alumina deposited using ozone (TFT B). While TFT A was affected by the pre‐vacuum annealing of GI, which resulted in Vth instability under NBS, TFT B did not show a difference after the pre‐vacuum annealing of GI. All the TFTs showed negative‐bias‐enhanced photo instability.