• 한국정보디스플레이학회:학술대회논문집
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• 2003.07a
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• pp.43-49
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• 2003

Low-temperature polysilicon (LTPS) technology has continued to mature with the passing of each year since LTPS mass production began. The integration of complex circuits has become possible with advances in microprocessing, leading to the realization of panels with highly advanced functions. At the same time, efforts have been made to meet market demands for lower costs, thereby boosting competitive strength. Today, LTPS-TFT LCDs have become standard equipment for the monitors of digital still cameras, and inroads are being made into the massive cellular phone market. Micro displays such as electronic viewfinders, which were previously only possible with high-temperature polysilicon technology, can now also be made with LTPS, thus expanding the scope of the technology. AMOLED displays using the LTPS-TFT as a back plane are also approaching the stage of industrialization. The hidden potential for the OLED to replace the familiar LCD has prompted Widespread anticipation for this emerging technology. This paper reflects on the history of LTPS technology, then looks forward to its future prospects and suggests a variety of potential fields of application.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.189-189
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• 2010

최근 연구와 생산에 가속이 붙기 시작한 AMOLED는 모두 LTPS TFT를 사용하고 있다. LTPS TFT는 높은 전자 이동도를 가지고 있기 때문에 현재 각광 받는 AMOLED에 잘 맞는다. 하지만 LTPS TFT는 균일성이 낮고 고비용이라는 문제점이 있으며, 현재 대면적 기술이 부족한 상태이다. 극복방안으로 AMOLED를 타겟으로 하는 Oxide TFT와 a-Si TFT의 기술이 발전되고 있다. Oxide TFT는 AMOLED backplane으로 사용될 수 있는 강력한 후보 중의 하나이다. Oxide TFT는 단결정 산화물과 다결정 복합 산화물 두 가지 범주를 가지고 있다. 본 연구에서는 다결정 Oxide TFT의 하나인 ZTO TFT를 연구함으로서 Engineer의 근본적 이슈인 저비용에 초점을 맞추어 소자특성을 확인해보도록 한다. n-type wafer 에 PE-CVD 장비를 이용하여 SiNx를 120 nm 증착하고, channel layer인 ZTO 용액을 spin-coating을 이용하여 형성하였다. 균일하게 형성된 ZTO의 결정을 위하여 $500^{\circ}C$에서 1시간 동안 공기 중에서 annealing을 하였다. 과정을 거친 ZTO는 약 30 nm 두께로 형성되었다. Thermal evaporator를 이용하여 Source, Drain의 전극을 형성 하고, wafer 뒷면에는 Silver paste를 이용하여 Gate를 형성하였다. 제작된 소자를 dark room temperature 에서 측정 하였다. 측정된 소자는 우수한 전기적 특성과 0.96 cm2/Vs 인 이동도를 얻어냈다. 이러한 소자의 안정성에 따른 전기적 특성을 관측하기 위하여 상온에서 $100^{\circ}C$ 까지의 온도 스트레스를 주었다. Stress에 따른 소자는 상온에서 시작하여 온도가 올라갈수록 이동도가 낮아지고, 문턱전압 증가와 SS이 커짐을 알 수 있었다. 캐리어의 운동 매커니즘에서 온도가 올라가면 격자진동의 영향을 크게 받음으로서 캐리어의 이동도가 낮아져 전기적 특성이 낮아지는 점이 본 연구에도 적용됨을 알 수 있었다. 본 연구를 통하여 화학적 안정성을 지닌 소자라는 점과 더불어 여타 TFT공정에 비하여 현저히 낮은 공정비용을 통하여 AMOLED가 요구하는 수준의 특성에 가까운 소자를 제작할 수 있다는 것을 확인하였으며 앞으로의 추가적인 연구에 따라서 더욱 완성된 공정기술을 기대할 수 있었다.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.205-207
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• 2008

The new process for hybrid silicon thin film transistor (TFT) using DPSS laser has been developed for realizing both low-temperature poly-Si (LTPS) TFT and a-Si:H TFT on the same substrate as a backplane of active matrix liquid crystal display. LTPS TFTs are integrated on the peripheral area of the panel for gate driver integrated circuit and a-Si:H TFTs are used as a switching device for pixel in the active area. The technology has been developed based on the current a-Si:H TFT fabrication process without introducing ion-doping and activation process and the field effect mobility of $4{\sim}5\;cm^2/V{\cdot}s$ and $0.5\;cm^2/V{\cdot}s$ for each TFT was obtained. The low power consumption, high reliability, and low photosensitivity are realized compared with amorphous silicon gate driver circuit and are demonstrated on the 14.1 inch WXGA+ ($1440{\times}900$) LCD Panel.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.641-644
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• 2008

Traditional LTPS TFT needs additional LDD process to decrease leakage current. However the fabrication process is no suitable for PI substrate. Additional laser multi-irradiation will damage the poly-Si to cause the TFT electrical degrade. Therefore we propose the simplified process to activate the $N^+$ and $N^-$ at the same time.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1111-1114
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• 2006

We have developed a 2 inch LTPS-TFT AMOLED display with a top emission structure on a $50-{\mu}m-thick$ metal foil. The Active matrix back planes were fabricated with the p-channel LTPS TFT with a conventional pixel circuit consisting of 2 transistors and 1 capacitance. The p-channel TFTs on the metal foil exhibited the field-effect mobility of $22cm^2/Vs$. Finally, a images from prototype monochrome AMOLED displays are successfully presented, with $64{\times}88$ pixels and 56-ppi resolution.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.124-128
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• 2004

A Poly-Si and a ITO films with surface roughness 1.8 nm and 0.5 nm of root mean square ($R_{rms}$ vakue) values were developed, respectively. A 3 inch UXGA LTPS TFT-LCD with 667 ppi resolution and a 10 inch VGA LTPS OLED have been developed and demonstrated using PMOS technology.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.10
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• pp.34-41
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• 2010

We proposed the new pixel compensation circuit with high aperture ratio and the driving method for the large-area, low-power AMOLED applications in this study. We designed with the low-temperature poly-silicon(LTPS) thin film transistors(TFTs) that has poor uniformity but good mobility and stability. To lower the error rate of the pixel circuit and to improve the aperture ratio for bottom emission method, we simplified the pixel compensation circuit. Because the proposed pixel compensation circuit with high aperture ratio has very low contrast ratio for conventional driving methods, we proposed the new driving method and circuit for high contrast ratio. Black data insertion was introduced to improve the characteristics for moving images. The pixel circuit was designed for 19.6" WXGA bottom-emission AMOLED panel, and the average aperture ratio of the pixel circuit is improved from 33.0% to 41.9%. For the TFT's $V_{TH}$ variation of ${\pm}0.2\;V$, the non-uniformity and contrast ratio of the designed panel was estimated under 6% and over 100000:1 respectively.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.4
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• pp.45-52
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• 2009

We proposed a new pixel circuit and driving method for the large-area, high-luminance AMOLED applications in this study. We designed with the low-temperature poly-silicon(LTPS) thin film transistors(TFTs) that has poor uniformity but stable characteristic. To improve the uniformity of an image, the threshold voltage($V_{TH}$) and the mobility of the TFTs can be compensated together. The proposed method overcomes the previous methods for mobility compensation, and that is profitable for large-area applications. Black data insertion was introduced to improve the characteristics for moving images. AMOLED panel can operate in two compensation mode, so the luminance degradation by mobility compensation can be released. The scan driver for controlling the pixel circuits were optimized, and the compensation mode can be controlled simply by that. Final driving signal has large timing margin, and the panel operates stably. The pixel circuit was designed for 14.1" WXGA top-emission ANGLED panel. The non-uniformity of the designed panel was estimated under 5% for the mobility compensation time of 1us.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.1015-1018
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• 2004

We proposed a new cross-coupled level shifter circuit using low temperature poly-Si(LTPS) TFT. The proposed level shifter can operate on low input voltage in spite of low mobility and widely varying high threshold voltage of LTPS TFT. Also, the proposed level shifter operates at high frequency and reduces power consumption for having fast rising and falling time and shortening period flowing short-circuit currents.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.533-536
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• 2006

VIATRON TECHNOLOGIES has developed Field-Enhanced Rapid Thermal Processor (FERTP) system that enables LTPS LCD and AMOLED manufacturers to produce poly-Si films at low cost, high throughput, and high yield. The FE-RTP allows the diverse process options including crystallization, thermal oxidation of gate oxides and fast pre-compactions. The process and equipment compatibility with a-Si TFT lines is able to provide a viable solution to produce poly-Si TFTs using a-Si TFT lines.