Size Effects of Poly-Si Formed by Laser Annealing With Periodic Intensity Distribution on the TFT Characteristics

Abstract

Currently, low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs), which are characterized by high mobility of electrons, are fabricated by excimer laser annealing. High mobility in low-temperature polycrystalline silicon is achieved by controlling the grain size to approximately 300 nm. However, with future potential growth of active-matrix organic light-emitting diodes in terms of their increasing use as backlight in active matrix micro-LEDs, even higher mobility is required. One of the methods to improve mobility is to produce grains of sizes above 300 nm. However, as far as we know, there are no reports of investigating the dependence between the device characteristics and the grain size of above 300 nm. In this study, we examine the possibility of controlling the grain size above approximately 350 nm by laser annealing with an intensity distribution and investigate the grain size dependence of the TFT characteristics. We show that the grain size can be controlled approximately in the range of 1-2.5 µm, and mobility of 248±28 cm 2 V -1 s -1 is achieved at a grain size of 2.5 µm. Furthermore, we compare the device characteristics of the stepand-repeat and scan annealing and verify that the device characteristics do not deteriorate even during scan annealing. The study confirms that it is technically possible to produce LTPS with grain sizes controlled in the range of 1-2.5 µm for customizing device characteristics.

Threshold voltage uniformity improvement by introducing charge injection tuning for low-temperature poly-Si thin film transistors with metal/oxide/nitride/oxide/silicon structure

“…The merits of LTPS TFTs compared with other TFTs, such as amorphous Si (α-Si) TFTs and amorphous oxide semiconductor (AOS) TFTs, include higher mobility, the ability to fabricate CMOS structures and better stability. However, threshold voltage (V T ) variation for LTPS TFTs, [6][7][8] which stems from the polycrystalline structure of LTPS film, is generally worse than that for α-Si and AOS TFTs with amorphous channel materials. Because V T variation induces brightness variation between pixels, especially for organic light-emitting displays as well as μ-LED displays where luminance is controlled by TFT channel current, a V T -compensation circuit with additional TFTs is needed, 9,10) which limits further improvement of display performance.…”

Nanosecond time-resolved two-dimensional temperature estimation of nanosecond laser-irradiated silicon

“…In recent years, lasers have been used in various fields such as cutting, welding, annealing, and doping owing to the improved performance of laser devices. Among these processing techniques, nanosecond pulsed lasers are used in laser annealing [1] and laser doping [2]. In the area irradiated by a nanosecond pulsed laser, the temperature changes rapidly on a nanosecond scale, which affects properties of the processed material.…”

Thin-film transistor arrays for biological sensing systems

“…The common fabrication process of OTFT is solution process or thermal evaporation; the OTFT device has the advantages of low cost and flexibility, but insufficient in the performance uniformity and device stability [19][20][21]. The common fabrication process of LTPS TFT is PECVD alone with the laser annealing; the LTPS TFT devices have a higher carrier mobility, while the uniformity is sort of poor, thus a uniformity compensation design is often required [22][23][24]. The common fabrication process of oxide TFT is sputter; this device has the advantages of appropriate uniformity, high carrier mobility, and low off current, but the process repeatability is relatively poor, which is a main factor hindering its commercial application [25][26][27].…”