Weijing Wu

A New Voltage-Programmed Pixel Circuit for Enhancing the Uniformity of AMOLED Displays

This letter presents a new voltage-programmed pixel circuit for the active-matrix organic light-emitting diode (AMOLED) displays, which consists of one driving thin-film transistor (TFT), four switching TFTs, two capacitors, and three control signal lines. The proposed pixel circuit can effectively compensate for the threshold-voltage shift of the driving TFT and the OLED degradation, which is verified by the simulation work using SMART-SPICE software. It is shown that the average nonuniformity of the OLED current for the proposed pixel circuit is 5.7% compared with 85.7% for the conventional 2T1C pixel circuit, and thus, the brightness uniformity of AMOLED displays can be enhanced. Moreover, a high contrast ratio can be achieved by the proposed pixel circuit since the OLED does not emit any light except for the emission period.

Coffee-Ring Defined Short Channels for Inkjet-Printed Metal Oxide Thin-Film Transistors

Short-channel electronic devices several micrometers in length are difficult to implement by direct inkjet printing due to the limitation of position accuracy of the common inkjet printer system and the spread of functional ink on substrates. In this report, metal oxide thin-film transistors (TFTs) with channel lengths of 3.5 ± 0.7 μm were successfully fabricated with a common inkjet printer without any photolithography steps. Hydrophobic CYTOP coffee stripes, made by inkjet-printing and plasma-treating processes, were utilized to define the channel area of TFTs with channel lengths as short as ∼3.5 μm by dewetting the inks of the source/drain (S/D) precursors. Furthermore, by introduction of an ultrathin layer of PVA to modify the S/D surfaces, the spreading of precursor ink of the InOx semiconductor layer was well-controlled. The inkjet-printed short-channel TFTs exhibited a maximum mobility of 4.9 cm(2) V(-1) s(-1) and an on/off ratio of larger than 10(9). This approach of fabricating short-channel TFTs by inkjet printing will promote the large-area fabrication of short-channel TFTs in a cost-effective manner.

A Compact Model for Polysilicon TFTs Leakage Current Including the Poole–Frenkel Effect

Based on a generation-recombination model including the Poole-Frenkel (PF) effect and phonon-assisted tunneling, numerical analysis shows that the logarithm of generation rate for polysilicon thin-film transistors (poly-Si TFTs) working in the leakage region is linear with the square root of lower electric field and approximately linear with higher electric field over a wide temperature range (273-423 K). Therefore, an analytical expression is found to approximate the generation rate. Furthermore, a compact model for poly-Si TFT leakage current including the PF effect is developed in this paper. The proposed model is analytical without numerical calculation, and its parameters can be extracted from experimental data; hence, it is attractive for circuit simulation. The model has been verified by comparing simulated results with experimental data.

Total Dose Ionizing Radiation Effects in the Indium–Zinc Oxide Thin-Film Transistors

This letter deals with the total dose ionizing radiation effects in the amorphous indium-zinc oxide thin-film transistors (IZO TFTs). After radiation, a negative shift of threshold voltage was observed. The experimental results show electron field effect mobility, subthreshold swing, and low frequency noise were increased after radiation. Furthermore, the influences of bias and gate length on the radiation effect of IZO TFTs are also presented.

An AC Driving Pixel Circuit Compensating for TFTs Threshold-Voltage Shift and OLED Degradation for AMOLED

This paper presents an ac driving pixel circuit for active-matrix organic light-emitting diode (AMOLED) displays, which is composed of one driving thin-film transistor (TFT), three switching TFTs and one capacitor. The proposed pixel circuit can not only make OLED work at the ac driving mode, but also effectively compensate for the threshold-voltage shift of the driving TFT and the degradation of OLED. Simulation results show that the nonuniformity of the proposed pixel circuit is significantly reduced (<; 10%) with an average value of 4.2% compared with that of the conventional 2T1C pixel circuit, and thus, the brightness uniformity of AMOLED displays can be enhanced. Moreover, a high contrast ratio can be achieved by the proposed pixel circuit due to no light emitting except for the emission period, as well as a relatively high aperture ratio due to a small number of components.

A Highly Stable Biside Gate Driver Integrated by IZO TFTs

This brief presents a new gate driver integrated by In-Zn-O thin-film transistors (IZO TFTs), including a clock-controlled inverter and an additional stabilized module. The biside driving method is used in the proposed gate driver, which will be allocated on both sides of the panel to drive the odd and even lines of pixel array, respectively. Thus, the space symmetry of the panel can be fully utilized for high resolution displays. The output signal of the biside gate driver can be generated stably up to 480th stage with a good noise-suppressed characteristic. The measured power consumption for one stage of the proposed gate driver is 0.5 mW with the clock frequency as 50 kHz. It is shown that the proposed gate driver can output a 3-\(\mu \) s pulsewidth with a good stability under 120-h test. Furthermore, a 3-in demonstration panel of 320*480 AMOLED display by the IZO TFTs process is fabricated to verify the function of the proposed biside gate driver.

A Low-Power High-Stability Flexible Scan Driver Integrated by IZO TFTs

This brief presents a low-power high-stability scan driver integrated by In-Zn-O (IZO) TFTs on polyimide substrate. Observed from the experimental results of the scan driver with 48 stages, there is no distortion and good noise-suppressed characteristics for the output waveforms. In one stage of the proposed scan driver, there only needs a small TFT connected to clock signals by using a feedback inverter and a dc output module to minimize the dynamic power consumption. It is measured that the power consumption for one stage of the proposed gate driver is 18.3 μW at the output swing of 15.3 V and the clock frequency of 50 kHz. There is a good noise-suppressed characteristic and high stability for the proposed scan driver as shown from a 300-h test.

A new compensation pixel circuit with all-p-type TFTs for AMOLED displays

Abstract This paper presents a new pixel circuit with all-p-type TFTs for AMOLED displays. The proposed pixel circuit can effectively compensate for the threshold-voltage shift of the driving TFT, the degradation of OLED and the parasitic resistance of the power supply line. And thus, the brightness uniformity of AMOLED displays can be enhanced. It is shown that the nonuniformity of the OLED current with an average value of 7.3% can be achieved by the proposed pixel circuit, while that of the conventional 2T1C pixel circuit is 73%. Moreover, a high contrast ratio can be also obtained by the proposed pixel circuit since there is no light emitting except for the emission period.

Analytical Extraction Method for Density of States in Metal Oxide Thin-Film Transistors by Using Low-Frequency Capacitance–Voltage Characteristics

An analytical expression for density of trap states (DOS) related to the surface potential is derived from the Poissons equation and the surface potential corresponding to certain gate-source voltage is obtained by integrating the low-frequency capacitance-voltage characteristic. It is shown that the DOS for indium-zinc-oxide thin-film transistors (IZO TFTs) may be represented by the superposition of exponential deep states and exponential tail states with the density of deep/tail states (N_DA /N_TA) at the conduction edge as 1.2 × 10¹⁷ cm^-3·eV^-1/9.0 × 10¹⁷ cm^-3·eV^-1 and the characteristics energy of deep/tail states (E_DA /E_TA) as 5.0 eV/0.182 eV. These extracted parameters are further verified by the comparison of the measured transfer and output characteristics of IZO TFTs with the simulation results by a 2D device simulator ATLAS (Silvaco). Hence, this extraction method of DOS may be very useful for characterizing metal oxide TFTs since it is analytical, fast, and accurate.

Low-Power Bi-Side Scan Driver Integrated by IZO TFTs Including a Clock-Controlled Inverter

This letter presents a low power In-Zn-O thin-film transistors (IZO TFTs) scan driver including a clock-controlled inverter to avoid the direct current path compared with the conventional diode-connected inverter. The so-called bi-side scan driver is divided into two parts, laying on the two sides of panel to drive the odd lines and the even lines of pixel arrays, respectively. Due to a smaller duty ratio of the clock in the output section than that of clocks in the inner section, only one large size transistor is required for both charging and discharging the scan line, and the discharging speed is faster than that of other merging TFT methods because it is at the bootstrapped state for the whole driving phase. Experimental results show that the output signal of each stage for the proposed scan driver has no distortion and exhibits good noise-suppressed characteristics. It is also verified that the power consumption of the clock-controlled inverter can be significantly reduced compared with the conventional diode-connected inverter.