Browsing by Author "Chang, TK"

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A novel device structure for low-temperature polysilicon TFTs with controlled grain growth in channel regions
(2000)
Cheng, LJ
;
Lu, YL
;
Lin, CW
;
Chang, TK
;
Cheng, HC
In this paper, we demonstrate a novel device structure of low-temperature polysilicon thin-film transistors (LTPS TFTs) for AMLCD applications with using excimer-laser crystallization (ELC). The device structure consists of a thin channel and a thick source/drain. This structure has its merit in the process of ELC and is capable of improving TFTs' electrical characteristics. During excimer laser irradiation, this kind of recessed structure is able to build up localized lateral thermal gradients in the regions near the steps and entice crystallization from the chiller thick source/drain regions toward the hotter thin channels. Because of the development of crystallization process, the average field-effect mobility of the devices can be increased to about 350 cm(2)/V.s, and the on/off current ratios exceed eight orders. In addition to improvement of device performance, the process window of ELC is broadened with the recessed structure.
A novel dual focus objective lens for DVD/CD pick-up head
(1998-03-01)
Liu, PY
;
Shieh, HPD
;
Ju, JJ
;
Tsai, ST
;
Yang, TM
A new dual focus objective lens of combinig aspherical surfaces of DVD and CD for DVD/CD pick-up head was designed. Numerical analysis based on the diffraction model were studied to trade off the spot size, side lobe, and energy ratio of DVD and CD, The hybrid aspherical surfaces of DVD and CD are optimized for low aberration. The spot size of full wave half maximum (FWHM) are 0.553 and 0.88 mu m for DVD and CD, respectively, measured from thus constructed double rings lens.
A novel germanium doping method for fabrication of high-performance p-channel poly-Si1-xGex TFT by excimer laser crystallization
(2003-04-01)
Chang, TK
;
Chu, FT
;
Lin, CW
;
Tseng, CH
;
Cheng, HC
In this letter, a novel process for fabricating p-channel poly-Si1-xGex thin-film transistors (TFTs) with high-hole mobility was demonstrated. Germanium (Ge) atoms were incorporated into poly-Si by excimer laser irradiation of a-Si1-xGex/poly-Si double layer. For small size TFTs, especially when channel width/length (W/L) was less than 2 mum/2 mum, the hole mobility of poly-Si1-xGex TFTs was superior to that of poly-Si TFTs. It was inferred that the degree of mobility enhancement by Ge incorporation was beyond that of mobility degradation by defect trap generation when TFT size was shrunk to 2 mum/2 mum. The poly-Si0.91Ge0.09 TFT exhibited a high-hole mobility of 112 cm(2)/V-s, while the hole mobility of the poly-Si counterpart was 73 cm(2)/V-s.
A novel laser-processed self-aligned gate-overlapped LDD poly-Si TFT
(2002-03-01)
Lin, CW
;
Tseng, CH
;
Chang, TK
;
Lin, CW
;
Wang, WT
A novel process for fabricating self-aligned gate-overlapped LDD (SAGOLDD) poly-Si thin film transistors (TFTs) was demonstrated. Laser Irradiation for dopant activation was performed from the backside of the quartz wafer. The graded LDD structure was naturally formed under the gate edges due to the lateral diffusion of the dapants during the laser activation. In comparison with the conventional laser-processed self-aligned poly-Si TFTs, the SAGOLDD poly-Si TFTs exhibited lower leakage current, suppressed kink effect, and higher reliability. Moreover, the proposed process was simple and very suitable for low-temperature process.
An investigation of bias temperature instability in hydrogenated low-temperature polycrystalline silicon thin film transistors
(2002-09-01)
Lin, CW
;
Tseng, CH
;
Chang, TK
;
Chang, YH
;
Chu, FT
The instability mechanisms of the hydrogenated n-channel low-temperature polycrystalline silicon thin film transistors under on-state stress were investigated with various bias stress conditions and device channel widths. It was found that hot carrier degradation which originated from a high drain electric field and self-heating during high current operation were the two dominant mechanisms responsible for device degradation. An electrically reversible depassivation/passivation phenomenon was also found in devices under high current stress. but not in those under hot carrier stress. It was inferred that the self-heating effect would accelerate the bond breakage and diffusion of hydrogen ions, thus enhancing the rate of depassivation/passivation. Moreover. when the Current in the hot carrier stress mode was sufficiently high. self-heating became the dominant degradation mechanism and hot carrier degradation phenomenon was also suppressed for devices with large channel width, Meanwhile, the electrically reversible depassivation/passivation phenomenon also occurred in this case.
Degradation of passivated and non-passivated N-channel low-temperature polycrystalline silicon TFTs prepared by excimer laser processing
(2002-08-01)
Teng, TH
;
Huang, CY
;
Chang, TK
;
Lin, CW
;
Cheng, LJ
The instability mechanisms of passivated and non-passivated low-temperature polycrystalline silicon thin film transistors (LTPS TFTs) under various bias stress conditions have been investigated. Irrespective of plasma treatment, the degradation was more severe under negative gate bias stress than that under positive gate bias stress. This could be due to Fowler-Nordheim tunneling electron induced impact ionization. For hot carrier stress, TFTs with NH3 plasma treatment degraded more severely than those without plasma treatment. This might be attributed to collapsing of weak Si-H bonds in NH3-plasma passivated devices. For the high current stress, it showed the opposite results against hot carrier stress. (C) 2002 Elsevier Science Ltd. All rights reserved.
Effects of excimer laser dopant activation on low temperature polysilicon thin-film transistors with lightly doped drains
(2001-11-01)
Tseng, CH
;
Lin, CW
;
Chang, TK
;
Cheng, HC
;
Chin, A
Excimer laser annealing has been utilized to manufacture low temperature polycrystalline silicon thin-film transistors with lightly doped drain (LDD) structures. The excimer laser annealing can effectively reduce the thermal budget of source/drain dopant activation, namely, without substrate heating. With the advantages of LDD structure, high performance device characteristics with a low "off" state current of 4.38 x 10(-12) A/mum, high on/off current ratio of 1.6 x 10(7). and good field-effect mobility of 268 cm(2)/V s. can be achieved simultaneously. (C) 2001 The Electrochemical Society.
Fabrication of low-temperature poly-Si thin film transistors with self-aligned graded lightly doped drain structure
(2002-01-01)
Cheng, HC
;
Lin, CW
;
Cheng, LJ
;
Tseng, CH
;
Chang, TK
A novel approach for fabricating low-temperature poly-Si (LTPS) thin film transistors (TFTs) with self-aligned graded lightly doped drain (LDD) structure was demonstrated. The self-aligned graded LDD structure was formed by side-etching the Al gate under the photoresist followed by excimer laser irradiation for dopant activation and lateral diffusion. The graded LDD poly-Si TFTs exhibited low-leakage-current characteristics without significantly sacrificing driving capability due to the graded dopant distribution in the LDD regions, in which the drain electric field could be reduced. The leakage current of 1 mum graded LDD UPS TFTs at Vds = 5 V and Vgs = -10 V could reach below 1 pA/mum, and the on/off current ratio at Vds = 5 V exceeded 10(7). (C) 2001 The Electrochemical Society.
High-performance poly-Si thin film transistors crystallized by excimer laser irradiation with a-Si spacer structure
(2005)
Chang, TK
;
Lin, CW
;
Tsai, CC
;
Lu, JH
;
Chen, BT
In this work, high-performance polycrystalline Si thin film transistors have been fabricated by excimer laser crystallization of an amorphous Si film deposited on an array of amorphous Si spacers. The amorphous Si spacers served as seeds for lateral growth during excimer laser irradiation. Large longitudinal grains could be found in the device channel regions. In consequence, the thin-film transistors fabricated with Si spacer structure exhibited a high field-effect mobility of 288 cm(2)/V-s while the mobility of the conventional counterpart was 129 cm(2)/V-s. In addition, the uniformity of the device performance was improved as lateral growth could be artificially controlled. (C) 2004 The Electrochemical Society.
Investigation of inductively coupled plasma gate oxide on low temperature polycrystalline-silicon TFTs
(2002-06-01)
Tseng, CH
;
Chang, TK
;
Chu, FT
;
Shieh, JM
;
Dai, BT
By optimizing the inductively coupled plasma (ICP) oxidation condition, a thin oxide of 10 nm has been grown at 350degreesC to achieve excellent gate oxide integrity of low leakage current < 5x10(-8) A/cm(2) (at 8 MV/cm), high breakdown field of 9.3 MV/cm and low interface trap density of 1.5x10(11)/eV cm(2). The superior performance poly-Si TFTs using such a thin ICP oxide were attained to achieve a high ON current of 110 μA/μm at V-D=1 V and V-G = 5 V and the high electron field effect mobility of 231 cm(2)/V.S.
Study on dopant activation of phosphorous implanted polycrystalline silicon thin films by KrF excimer laser annealing
(2002-08-01)
Tseng, CH
;
Lin, CW
;
Teng, TH
;
Chang, TK
;
Cheng, HC
The KrF excimer laser annealing of phosphorous implanted polycrystalline silicon (poly-Si) films had been investigated completely. Resistors were fabricated to measure sheet resistance of poly-Si film. The interference effect, heat absorption of capping oxide as well as transformation of poly-Si grain size during laser annealing were reported. Depending on the carrier concentrations, poly-Si exhibits different sheet resistance behavior when the excimer laser fluence is higher than the full-melt threshold fluence. The sheet resistance of poly-Si film has an abnormal increase from 5 x 10(4) to 4 x 10(6) Q/square when the excimer laser energy is higher than full-melt threshold energy. (C) 2002 Elsevier Science Ltd. All rights reserved.
Thickness dependence of microstructure of laterally crystallized poly-Si thin films and electrical characteristics of low-temperature poly-Si TFTs
(2003-08-01)
Chang, TK
;
Lin, CW
;
Chang, YH
;
Tseng, CH
;
Chu, FT
The effects of thickness of a-Si thin films on the resulting microstructure of metal-induced laterally crystallized (MILC) poly-Si and electrical characteristics of MILC low temperature poly-Si (LTPS) thin film transistors (TFTs) were investigated. The TEM images revealed a double-layer structure in the 1000-Angstrom MILC poly-Si thin film. However, for the 400-Angstrom MILC poly-Si thin film, there were single-layer grains within the thin film layer. The reason has been ascribed to the geometry restriction in the crystallization procedure. The average mobility of fabricated MILC LTPS TFTs with active layer thickness of 400 Angstrom showed a little higher than that with 1000 Angstrom active layer. Moreover, the MILC LTPS TFTs with active layer thickness of 400 Angstrom exhibited better electrical uniformity than those with 1000 Angstrom active layer either in threshold voltage or field-effect mobility. The reason should also be attributed to the different crystalline structures within the two thin-film layers. (C) 2003 The Electrochemical Society.