Novel a‐Si:H TFT pixel circuit for electrically stable top‐anode light‐emitting AMOLEDs

Abstract

Abstract— A novel pixel circuit for electrically stable AMOLEDs with an a‐Si:H TFT backplane and top‐anode organic light‐emitting diode is reported. The proposed pixel circuit is composed of five a‐Si:H TFTs, and it does not require any complicated drive ICs. The OLED current compensation for drive TFT threshold voltage variation has been verified using SPICE simulations.

P‐14: a‐IGZO TFT Based Pixel Circuits for AM‐OLED Displays

“…Authors have previously explored the possible application of a-InGaZnO TFTs to a current scaling pixel circuit that provides a wide dynamic OLED current (I OLED ) range and compensation abilities [8]. Here, we apply a-InGaZnO TFTs to a voltage-programmed pixel electrode circuit that has shown some enhancement with a-Si:H TFT [9]. Synopsys HSPICE simulation tool with the a-InGaZnO TFT and OLED…”

“…As shown in Figure 2, each pixel is composed of one power line (V DD ), two control lines (Gate1, Gate2), two capacitors (C st1 , C st2 ), and five TFTs; two switch TFTs (SW1, SW2), a pre-charge TFT (PC), a drive TFT (DR), and a mirror TFT (MR). The operation detail of this circuit can be found elsewhere [9]. Since the field-effect mobility of a-InGaZnO TFTs is about 10 times larger than that of a-Si:H TFTs, smaller device sizes (W/L = 5μm/5μm) and lower supply voltages (V DD = 10V) can be used for this circuit based on a-InGaZnO TFTs.…”

a‐InGaZnO thin‐film transistors for AMOLEDs: Electrical stability and pixel‐circuit simulation

“…An identical equation has also been derived for a-Si:H TFTs when subject to constant current stress, based on the carrier-induced defect creation model. 4 (5) where α and β are the exponents for the gate overdrive voltage and stress time, respectively, τ = τ 0 exp(E τ /kT STR ), and E τ is the average effective barrier that the electrons in the a-InGaZnO channel need to overcome before they can enter the insulator, and τ 0 is the thermal prefactor for emission over the barrier. This power-law relation shows that there is no upper bound for ∆V T which is in contrast to the stretched-exponential model.…”

“…Larger devices and more-complex pixel circuits are needed to realize acceptable a-Si:H TFT AMOLEDs, which greatly limits the display resolution. 5,6 As a result, TFTs based on other semiconductor materials have been explored as an alternative approach to realize reliable, high-resolution AMOLEDs. [7][8][9] Above all, amorphous In-Ga-Zn-O (a-InGaZnO) TFTs possess certain advantages including visible transparency, low processing temperature, good uniformity, adequate mobility, low off-current, sharp subthreshold swing, and potentially better electrical stability, which make them very attractive for AMOLEDs.…”

P‐14: AM‐OLED Pixel Circuits Based on a‐InGaZnOThin Film Transistors

“…2. SPICE parameters were extracted based on experimental data obtained within our group [11], and summarized in Table 1. The OLED area was assumed to be 12000μm 2 which is about the subpixel area of an RGB 3" QVGA display (63.5μm x 190.5μm).…”