V _th compensated AMOLED pixel employing dual-gate TFT driver

Abstract

A simple active-matrix organic light-emitting diode (AMOLED) pixel with conventional voltage driving and ability to compensate for the V th shift of thin-film transistors (TFTs) is proposed. The stable pixel operation is achieved by the employment of a dual-gate TFT for OLED driving. Simulation results also show that a new pixel exhibits almost linear programming I -V characteristics, whereas a conventional pixel design features a highly nonlinear behaviour.Introduction: Displays with active-matrix organic light-emitting diodes (AMOLEDs) are considered as the next generation display technology because of their superb image quality, digital addressing, self-emissive nature and low energy consumption [1]. A conventional AMOLED pixel has two thin-film transistors (TFTs) for switching and driving and one capacitor (2T1C). If subjected to a prolonged gate bias stress, the widely used TFTs including CdSe, amorphous and/or polysilicon devices are prone to electrical instabilities, most notably the positive V th shift [2]. If not compensated for, this shift will yield to a substantial OLED current degradation and the pixel brightness decay. So far, several V th compensation methods in 2TC1 pixels [3-5] have been described, but they require either non-conventional complex voltage driving schemes [3,5] or an excessively long programming period [4]. In this Letter, a novel V th shift compensated 2T1C pixel is proposed, which maintains a conventional voltage driving scheme for compatibility with well developed LCD display driver ICs.

Boosted Gain of the Differential Amplifier Using the Second Gate of the Dual-Gate a-IGZO TFTs

“…These transfer curves exhibit parallel shifts at different V TG values. Those phenomena are attributed to the attraction and expelling of free carriers in the active layer by the top gate, which is well explained in [6]. It provides a way of using the bottom gate of the dual-gate a-IGZO TFT as the primary gate while controlling the top gate independently.…”

“…Taking advantage of the fact that the threshold voltage V th of the dual-gate a-IGZO TFT can be shifted by the top gate of the TFT [5], [6], we are able to design the circuit with more flexibility. In fact, some new circuits utilizing the dual-gate TFTs were proposed [3], [7]- [13].…”

56.4: Dual‐Gate IGZO TFT for Threshold‐ Voltage Compensation in AMOLED Pixel Circuit

“…However, they have some drawbacks such as the current driving scheme [17], the need of both n and p type TFTs [18], individual driving of the anode and the cathode of OLED [19], or indirect voltage driving through capacitive coupling [20]. Taking the advantage of the fact that the Vth of dual-gate amorphous InGaZnO4 (a-IGZO) TFT can be controlled by the second gate of the TFT [21][22], N.D. Jankovic and V. Brajovic et al proposed a pixel circuit [23], but it is based on a premise that the effect of the second gate on the Vth of the dual-gate TFT is constant, which is not necessarily true.…”

7-4: AMOLED Pixel Circuit using Dual Gate a-IGZO TFTs for Simple Scheme and High Speed VTHExtraction

“…1(a)). Jankovic et al has suggested simple a 2T1C (two TFTs and one capacitor) circuit but, optimum design is needed to get appropriate performance of compensation [12]. Tai et al has also implemented using simple 3T2C circuit, which uses top (auxiliary)-gate sweep to extract V TH of TFT for compensation.…”