P-12: 3-D TCAD Simulation for Describing Intrinsic Fluctuations in Polycrystalline Silicon Thin Film Transistors

Abstract

In this work, we investigate the influence of grain boundaries on the performance of polycrystalline silicon thin-film transistors (poly-Si TFTs) for high resolution active-matrix organic light-emitting diode (AMOLED) displays using Voronoi diagram. The novel 2-D Voronoi polycrystalline grain structure can show a more realistic electrical parameter variability when the channel dimension is scaled down for high-resolution display. Using a proposed method, the impact of polycrystalline granular structure controlled by crystallization process is identified. Further, we predict the effect of grain boundary-induced variations under different laser annealing process, such as Excimer Laser Annealing (ELA).

Effects of TFT mobility variation in the threshold voltage compensation circuit of the OLED display

“…As mentioned earlier, the difference of |V GS.M1 | between the two cases had an almost constant value (0.17 V) in all the OLED current cases (1, 10, and 100 nA). The OLED current of the double-mobility case, however, could be larger or smaller compared with the reference case because the mobility as well as the V GS determined the current simultaneously according to Equation (1). When the OLED current of the reference case was 10 nA, there was little difference, although the mobility was doubled.…”

“…Therefore, a pixel circuit is needed to compensate for the TFT non-uniformity and to have a uniform voltage-to-brightness relation. For example, in the case of the low-temperature polycrystalline silicon (LTPS) TFT, the device parameters such as the carrier mobility, threshold voltage (V th ), and subthreshold swing vary depending on the random distribution of the grain boundaries in the polycrystalline silicon (poly-Si) film [1,2]. The conventional pixel circuits are designed to compensate only for the variation of the V th of the TFT [3][4][5][6][7][8].…”

“…Reported in this paper is how the compensatedfor OLED current varies when the mobility of the TFT increases in the conventional V th compensation circuit. Figure 1 shows Choi's 6T1C V th compensation circuit, which was used in the analysis [1]. This circuit has been used in the Samsung smartphones for nearly 10 years.…”

Organic light‐emitting diode display pixel circuit employing double‐gate low‐temperature poly‐Si thin‐film transistor and metal‐oxide thin‐film transistors

“…Therefore, a compensation circuit is necessary in each pixel of the LTPS-based OLED display to compensate for the nonuniform characteristics of the LTPS TFTs. [9][10][11][12] Mura on the OLED display is not completely resolved even with the compensation circuit. Moreover, it tends to be severe as the current level in each pixel decreases with increasing OLED efficacy and with decreasing pixel size.…”

“…However, the LTPS TFT exhibits poor uniformity. Therefore, a compensation circuit is necessary in each pixel of the LTPS‐based OLED display to compensate for the nonuniform characteristics of the LTPS TFTs 9–12 …”