This letter presents a new pixel design and driving method for active-matrix organic light-emitting diode (AMOLED) displays using low-temperature polycrystalline silicon thin-film transistors (TFTs). The proposed pixel circuit consists of five TFTs and one capacitor to eliminate the variation in the threshold voltage of the TFTs, and the drop in the supply voltage in a single frame operation by the source-follower-type connection and the bootstrap. The proposed pixel circuit has been verified to realize uniform output current by the simulation work using the HSPICE software. The novel pixel design has great potential for use in large-size and high-resolution AMOLED displays.Index Terms-Active-matrix organic light-emitting diode (AMOLED), current-resistance (IR) drop, pixel design, polycrystalline silicon thin-film transistors (poly-Si TFTs), uniformity.

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The degradation of n-channel poly-silicon thin film transistor ͑poly-Si TFT͒ has been investigated under dynamic voltage stress. The ON-current of TFT is 0.03 times the initial value after 1000 s stress. However, both the sub-threshold swing and threshold voltage almost kept well during the ac stress. The current crowding effect was rapidly increased with the increasing of stress duration. The creation of effective trap density in tail-states of poly-Si film is responsible for the electrical degradation of poly-Si TFT. Moreover, the damaged regions were evidenced to be mainly near the source/drain regions according to the electrical analyses.Low-temperature polycrystalline-silicon thin film transistors ͑poly-Si TFTs͒ have been widely investigated for flat-panel applications such as active matrix liquid crystal display and active matrix organic light-emitting diode display. 1-4 Poly-Si TFTs can be fabricated on low-cost glasses because the maximum process temperature is lower than 600°C. The major advantage of the poly-Si TFT is a higher field effective mobility than that of the a-Si-based TFT. Moreover, the poly-Si TFT can be produced as complementary N-channel and P-channel transistors. Taking advantage of these features, poly-Si TFTs are applied for pixel TFTs and the driver circuits ͑e.g., scan driver͒. If the mobility of poly-Si TFTs is further increased, this poly-Si technology will realize the system on panel ͑SOP͒ which will integrate memory, CPU, and display. 5 However, the traps of grain structures play an important role for the electrical properties and stabilities of poly-Si TFTs. TFT devices in functional circuits serve as the switches and suffer the high-frequency voltage pulses. Previous research reports have shown a relationship between the creation of states and hot-carriers effect by performing dc stress. 6,7 The degradation mechanism of n-channel TFT under dynamic voltage stress, however, has not yet been clarified. 8,9 The degraded TFT will seriously influence the operation of the circuits. In this study, the degradation under dynamic operation for poly-Si n-channel TFT will be investigated by electrical analysis in detail. ExperimentalN-channel poly-Si TFTs with top-gate structure were fabricated on a glass substrate without lightly doped drain ͑LDD͒. First, a 50 nm thick amorphous silicon ͑a-Si͒ film was deposited by plasmaenhanced chemical vapor deposition ͑PECVD͒, and, subsequently, the films were dehydrogenated by furnace annealing. After dehydrogenation, the a-Si films were crystallized by XeCl excimer-laser. The power of the line-shaped beam was 350 mJ/cm 2 . Following the laser process, 100 nm thick gate oxide was deposited by PECVD. Then, the implantation was adopted to define the source/drain ͑S/D͒ region. Then an annealing process was performed to activate the dopant impurities. MoW was sputtered as a gate metal. The dimensions of TFTs in this work were L = 9 m, W = 6 m and the overlap of gate metal and S/D junction is 1 m. The cross-sectional views of TFTs were illustrated in Fig. 1...

In this paper, we discuss the threshold voltage instability of two distinct layouts of hydrogenated amorphous silicon thin film transistors (a-Si:H TFTs). By simultaneously applying gate and drain bias stress, we show that the average threshold voltage shift of circular a-Si:H TFTs is 54% less than that of conventional inverted staggered a-Si:H TFTs. This result is primarily due to that the circular layout reduces the channel electron concentration. ISE-DESSIS (Integrated System Engineering DEvice Simulation for Smart Integrated Systems) was used to simulate the parallel electric field and obtain the total channel electron concentration. The simulation results closely correspond to the explanation in this study. These results indicate a significant impact of improving threshold voltage stability by a layout method.

A new pixel design and driving method for active-matrix organic light-emitting diode (AMOLED) display using low-temperature polycrystalline silicon thin-film transistor (LTPS-TFT) is proposed. The new circuit consists of five TFTs and one capacitor to eliminate the variation in the threshold voltage of the TFTs, and the drop in the supply voltage in a single frame operation. The proposed pixel circuit has been verified to realize uniform output current by the simulation work using HSPICE software. The simulated error rate of the output current is also discussed in this paper. The novel pixel design has great potential for use in large size and high resolution AMOLED displays.