Search

Recent commercial success of high-resolution AMLCDs and AMOLED displays has led to accelerated adoption and scale-up of ELA, the preferred technique for creating LTPS films. Here, key aspects of the process are discussed; in particular, the formation of laser-induced periodic surface structures (LIPSS) and the super-lateral growth (SLG) phenomenon. Also, a novel upright-microscopy technique is described for characterization of ELA-processed films.

Herein is provided an improved method of sequential lateral solidification of crystalline semiconductor film. The improvement consists of using a pulse laser to create two distinct zones of molten crystals. The laser creates these zones by laterally and in stepwise fashion moving the substrate film beneath it. The crystals form predetermined patterns as they cool. A computer program in memory controls the movement of the substrate film.

The case for thin-film polycrystalline silicon (pc-Si) solar cells is strong as it combines the cost benefit of thin-films and the quality potential of crystalline Si technology. The challenge is in making high-quality pc-Si layers on non-Si substrates. By studying layers based on aluminum-induced crystallization (AIC) we previously showed that electrically active intragrain defects are a major limiting factor for thin-film polycrystalline silicon solar cells. This paper investigates the use of a recently proposed novel scanning-laser based mixed-phase solidification (MPS) process which results in large grains with a low intragrain defect density, as well as a narrow grain size distribution and strong surface crystallographic texture [6]. Through subsequent epitaxial growth, absorber layers with the desired doping and thickness can be obtained. Defect etching and TEM measurements demonstrate the drastically decreased intragrain defect density compared to the AIC-based samples. The most efficient solar cell so far has an energy conversion efficiency of 5.4% and open circuit voltage (V oc ) of around 500mV. From the preliminary results obtained, we conclude that mixed phase solidification is an attractive technique to crystallize seed layers for thin-film silicon solar cells.

— CMOS TFT circuits were fabricated on plastic using sequential laterally solidified silicon combined with a low-temperature CMOS process. The unity-gain frequencies of the best of NMOS TFTs are greater than 250 MHz, and the CMOS ring oscillators operate at 100 MHz. To the best of the authors' knowledge, these are the highest-frequency circuits ever fabricated directly on plastic. This high-performance CMOS-on-plastic process can be applied to the fabrication of AMLCD integrated drivers and AMOLED pixels on plastic substrates.

We developed a CMOS-on-plastic technology using sequential lateral solidification to form LTPS TFTs. We have achieved unity-gain frequencies ft greater than 250 MHz, with CMOS ring oscillators operating at 100 MHz. To our knowledge these are the highest frequency transistors and circuits ever fabricated directly on plastic.

Thin film transistors fabricated using Low Temperature Polycrystalline Silicon (LTPS) have several well-known advantages over those made with amorphous Silicon: higher electron mobility, smaller size, higher speed. However, LTPS has not been widely adopted due to the relatively high cost and low yield of the process relative to a-Si. We have investigated a laser annealing process that offers an improvement for both throughput and yield when compared to existing processes. The process uses a very narrow laser beam (∼5 microns) at high repetition rates to create large poly-Si crystals via lateral growth. The beam length is long enough to allow the substrate to be scanned in a single pass, resulting in better uniformity without any seams seen in multi-pass techniques. In this presentation, we will present results from a prototype system used to validate the critical elements of the process.