Browsing by Author "Chen, TF"

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A novel four-mask-processed poly-Si TFT fabricated using excimer laser crystallization of an edge-thickened alpha-Si active island
(2004-06-01)
Chen, TF
;
Yeh, CF
;
Liu, CY
;
Lou, JC
;
電子工程學系及電子研究所
A novel four-mask-processed polycrystalline silicon thin-film transistor (poly-Si TFT) is fabricated using 50-pulse KrF excimer laser to crystallize an edge-thickened amorphous silicon (a-Si) active island without any shrinkage. This method introduces a temperature gradient in the island to enlarge grains from the edge, especially when the channel width is narrow. The grain boundaries across the width of the channel suppress the leakage current and the drain-induced barrier lowering. Moreover, the proposed poly-Si TFT with a channel length of L = 2 mum and a channel width of W = 1.2 mum possesses a high field-effect mobility of 260 cm(2)/Vs and an on/off current ratio of 2.31 x 10(8).
A tree-based inverted file for fast ranked-document retrieval
(2003)
Shieh, WY
;
Chen, TF
;
Chung, CP
;
資訊工程學系
;
Department of Computer Science
Inverted files are widely used to index documents in large-scale information retrieval systems. An inverted file consists of posting lists, which can be stored in either a document-identifier ascending order or a document-weight descending order. For an identfier-ascending-order posting list, retrieving ranked documents necessitates traversal of all postings, whereas for the weight-descending-order posting list, performing Boolean queries involves very complex processing. In this paper, we transform a posting list to a tree-based structure, called the n-key-heap posting tree, to speedup ranked-document retrieval for Boolean queries. In this structure, the orders of document identfiers and document weights are preserved simultaneously. To preserve the identifier order, the edge pointers are designed to maintain numerical order in the posting tree. To preserve the weight order, greater-weight postings are stored in higher tree nodes by the heap property. We model these criteria to a tree-construction problem and propose an efficient algorithm to construct an optimal posting tree having the minimal access time.
Branch-and-bound task allocation with task clustering-based pruning
(2004-11-01)
Ma, YC
;
Chen, TF
;
Chung, CP
;
資訊工程學系
;
Department of Computer Science
We propose a task allocation algorithm that aims at finding an optimal task assignment for any parallel programs on a given machine configuration. The theme of the approach is to traverse a state-space tree that enumerates all possible task assignments. The efficiency of the task allocation algorithm comes from that we apply a pruning rule on each traversed state to check whether traversal of a given sub-tree is required by taking advantage of dominance relation and task clustering heuristics. The pruning rules try to eliminate partial assignments that violate the clustering of tasks, but still keeping some optimal assignments in the future search space. In contrast to previous state-space searching methods for task allocation, the proposed pruning rules significantly reduce the time and space required to obtain an optimal assignment and lead the traversal to a near optimal assignment in a small number of states. Experimental evaluation shows that the pruning rules make the state-space searching approach feasible for practical use. (C) 2004 Published by Elsevier Inc.
Comparison of oxide breakdown progression in ultra-thin oxide SOI and bulk pMOSFETs
(2004)
Chan, CT
;
Kuo, CH
;
Tang, CJ
;
Chen, MC
;
Wang, TH
Accelerated oxide breakdown progression in ultra-thin oxide (1.4nm) SOI pMOSFETs is observed, as compared to bulk devices. The accelerated progression is explained by the increase of hole stress current as a result of breakdown induced channel carrier heating in a floating-body configuration. Numerical simulation of hole tunneling current and hot carrier luminescence measurement are carried out to justify the proposed theory.
Design and implementation of ultra-low latency optical label switching for packet-switched WDM networks
(2000-12-01)
Meagher, B
;
Chang, GK
;
Ellinas, G
;
Lin, YM
;
Xin, W
An ultra-low latency, high throughput internet protocol(IP) over wavelength division multiplexing (WDM) packet switching technology for next-generation internet (NGI) applications has been designed and demonstrated. This method overcomes limitations of conventional optical packet switching, which require buffering of packets and synchronization of bits, rind optical burst switching methods that require estimation of delays at each node and for each path. An optical label switching technique was developed to realize flexible bandwidth-on-demand packet transport on a reconfigurable WDM network. The aim was to design a network with simplified protocol stacks, scalability, and data transparency, This network will enable the NGI users to send their data applications at gigabit/second access speed with low and predictable latency (<1 sec per switch node), with a system capacity of beyond multi-Tb/s. Packet forwarding utilizes WDM optical headers that are carried in-band on the same wavelength and modulated out-of-hand in the frequency domain.
Effects of electrode materials and annealing ambients on the electrical properties of TiO2 thin films by metalorganic chemical vapor deposition
(1997-03-01)
Sun, SC
;
Chen, TF
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this work, we investigate the effects of the top electrode materials and annealing ambients on the electrical properties of chemical-vapor-deposited (CVD) TiO2 films. Experimental results indicate that the leakage current is mainly determined by the work function of electrode materials before sintering. The capacitor with TaN top electrode reveals the least leakage. After 450 degrees C and 800 degrees C sintering in N-2, owing to its thermal stability, WN is found to be the optimal material for withstanding high-temperature thermal treatment. From the annealing ambient results, N2O was more effective than O-2 in reducing leakage current, and furnace annealing in N2O (FN2O) produces the smallest leakage. Such a phenomenon is primarily owing to the reduction of oxygen vacancies and carbon concentration in TiO2 by the atomic oxygen generated by the dissociation of N2O during the thermal cycle, thereby improving film quality.
Effects of grain boundaries on performance and hot-carrier reliability of excimer-laser annealed polycrystalline silicon thin film transistors
(2004-05-15)
Chen, TF
;
Yeh, CF
;
Lou, JC
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This work examines the effects of grain boundaries on the performance and hot-carrier reliability of excimer-laser-annealed polycrystalline silicon thin film transistors (poly-Si TFTs) before and after NH3 plasma treatment. Self-aligned poly-Si TFTs, whose channel regions include a 150 nm thick laser-crystallized poly-Si layer with small grains and a 100 nm thick layer with large grains, are fabricated. Other TFTs, with large grains throughout their channels, are fabricated nearby for comparison. The trapping of electrons at grain boundaries in the drain junction creates strong local electric fields that boost the leakage current, cause the threshold voltage to decline as the drain bias increases, enhance the kink effect in the output characteristics, and degrade the hot-carrier reliability of devices. When static hot-carrier stress is applied to nonhydrogenated poly-Si TFTs for less than 10(4) s at V-GS=10 V and V-DS=20 V, hot holes are injected into the gate oxide at the same time trap states are created in the drain junction. The screening effect is observed when the same stress is applied to devices that have many grain boundaries in their drain junctions. NH3 plasma treatment prevents the trapping of electrons at grain boundaries. The performance of hydrogenated poly-Si TFTs improves, but the hot-carrier reliability of those TFTs with large grains in their drain junctions degrades. The hydrogenation causes a trade-off between the electrical characteristics and the hot-carrier reliability, and introduces irregular humps in the subthreshold region. (C) 2004 American Institute of Physics.
Fault-tolerant gamma interconnection networks by chaining
(2000-03-01)
Chen, CW
;
Lu, NP
;
Chen, TF
;
Chung, CP
;
資訊工程學系
The authors propose two single-fault-tolerant gamma interconnection networks. The first is a partially chained gamma interconnection network (PCGIN) with two disjoint paths between any source-destination pair. A PCGIN has the characteristics of one fault tolerance and destination tag routing, but backtracking may be necessary when a fault occurs. To eliminate the backtracking penalties of a PCGIN, a fully chained gamma interconnection network (FCGIN); that can at least tolerate one link or switch fault at each stage without backtracking, is also proposed FCGIN has the advantages of destination tag routing, lower hardware costs than a PCGIN, low fault penalty, and strong reroutability.
Inverted file compression through document identifier reassignment
(2003-01-01)
Shieh, WY
;
Chen, TF
;
Shann, JJJ
;
Chung, CP
;
資訊工程學系
The inverted file is the most popular indexing mechanism for document search in an information retrieval system. Compressing an inverted file can greatly improve document search rate. Traditionally, the d-gap technique is used in the inverted file compression by replacing document identifiers with usually much smaller gap values. However, fluctuating gap values cannot be efficiently compressed by some well-known prefix-free codes. To smoothen and reduce the gap values, we propose a document-identifier reassignment algorithm. This reassignment is based on a similarity factor between documents. We generate a reassignment order for all documents according to the similarity to reassign closer identifiers to the documents having closer relationships. Simulation results show that the average gap values of sample inverted files can be reduced by 30%, and the compression rate of d-gapped inverted file with prefix-free codes can be improved by 15%. (C) 2002 Elsevier Science Ltd. All rights reserved.
Investigation of grain boundary control in the drain junction on laser-crystalized poly-Si thin film transistors
(2003-07-01)
Chen, TF
;
Yeh, CF
;
Lou, JC
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This letter investigates the influences of grain boundaries in the drain junction on the performance and reliability of laser-crystalized poly-Si thin film transistors (TFTs). A unique test structure where the channel. region includes 150-nm-thick laser-crystalized poly-Si with, small grain sizes and a 100-nm-thick one with large grain sizes is fabricated. Different behaviors in the electrical characteristics and reliability of a single TFT are observed under measurements of the forward mode and then under first measurements of the reverse mode. This is due to the different number of, grain boundaries in the drain junction. Grain boundaries in the drain junction were found to cause reduced ON/OFF current ratio, variations in threshold voltage With drain bias, significantly, increased kink effect in the output characteristics, and poor hot-carrier stress endurance.
Leakage current reduction in chemical-vapor-deposited Ta2O5 films by rapid thermal annealing in N2O
(1996-07-01)
Sun, SC
;
Chen, TF
;
電子工程學系及電子研究所
;
奈米中心
;
Department of Electronics Engineering and Institute of Electronics
This study aims to improve the electrical characteristics and reliability of low-pressure chemical vapor deposited (LPCVD) Ta2O5 films by developing a new postdeposition single-step annealing technique. Experimental results indicate that excited oxygen atoms generated by N2O decomposition can effectively repair the oxygen vacancies in the as-deposited CVD Ta2O5 film, thereby resulting in a remarkable reduction of the film's leakage current. Two other post-deposition annealing conditions are compared: rapid thermal O-2 annealing and furnace dry-O-2 annealing. The comparison reveals that RTN(2)O annealing has the lowest leakage current, superior thermal stability of electrical characteristics and the best time-dependent dielectric breakdown (TDDB) reliability.
Leakage current reduction in chemical-vapor-deposited Ta2O5 films by rapid thermal annealing in N2O
(1996-07-01)
Sun, SC
;
Chen, TF
;
電子工程學系及電子研究所
;
奈米中心
;
Department of Electronics Engineering and Institute of Electronics
This study aims to improve the electrical characteristics and reliability of low-pressure chemical vapor deposited (LPCVD) Ta2O5 films by developing a new postdeposition single-step annealing technique. Experimental results indicate that excited oxygen atoms generated by N2O decomposition can effectively repair the oxygen vacancies in the as-deposited CVD Ta2O5 film, thereby resulting in a remarkable reduction of the film's leakage current. Two other post-deposition annealing conditions are compared: rapid thermal O-2 annealing and furnace dry-O-2 annealing. The comparison reveals that RTN(2)O annealing has the lowest leakage current, superior thermal stability of electrical characteristics and the best time-dependent dielectric breakdown (TDDB) reliability.
Negative substrate bias enhanced breakdown hardness in ultra-thin oxide pMOSFETs
(2003)
Wang, TH
;
Tsai, CW
;
Chen, MC
;
Chan, CT
;
Chiang, HK
Negative substrate bias enhanced breakdown hardness in ultra-thin oxide (1.4nm) pMOS is observed. This result is believed due to the increase of hole stress current during breakdown progression via breakdown induced carrier heating. Numerical analysis of substrate bias effect on hole tunneling current is performed to support the proposed theory. This phenomenon is particularly significant to gate oxide reliability in floating substrate (PD-SOI) or forward-biased substrate devices.
Posting file partitioning and parallel information retrieval
(2002-08-15)
Ma, YC
;
Chen, TF
;
Chung, CP
;
資訊工程學系
;
Department of Computer Science
The rapid growth in Internet usages brings new challenges on designing a scalable information retrieval system. To reduce the response time of a query to a large database, we parallelize both CPU computation and disk access of Boolean query processing on a cluster of workstations. The key issue is to partition the inverted file such that, during parallel query processing, each workstation consults only its own locally resident data to complete its task. To achieve this goal, we treat the set of all postings referring to a document ID as an object to be allocated in the develop data placement problem. Following the partitioning by document ID principle, we develop posting file partitioning algorithms to transform a sequential information retrieval system to a parallel information retrieval system. The advantage is that a better speed-up can be achieved by deriving from the fast sequential approach the compressed posting file. The partitioning schemes are designed to balance work-load of workstations in parallel query processing without increasing the average disk access time per posting. The experiment shows that almost linear speed-up can be achieved and the performance bottleneck in previous work, which parallelize only disk access, can be removed. This work shows that, by using parallel processing technique, it is feasible to build a scalable information retrieval system. (C) 2001 Elsevier Science Inc. All rights reserved.
Reduction of leakage current in chemical-vapor-deposited Ta2O5 thin films by furnace N2O annealing
(1997-06-01)
Sun, SC
;
Chen, TF
;
電子工程學系及電子研究所
;
奈米中心
;
Department of Electronics Engineering and Institute of Electronics
In this brief, we present a post-deposition annealing technique that employs furnace annealing in N2O (FN2O) to reduce the leakage current of chemical-vapor-deposited tantalum penta-oxide (CVD Ta2O5) thin films, Compared with furnace annealing in O-2 (FO) and rapid thermal annealing in N2O (RTN2O), FN2O annealing proved to have the lowest leakage current and the most reliable time-dependent dielectric breakdown (TDDB).
Reduction of leakage current in chemical-vapor-deposited Ta2O5 thin films by furnace N2O annealing
(1997-06-01)
Sun, SC
;
Chen, TF
;
電子工程學系及電子研究所
;
奈米中心
;
Department of Electronics Engineering and Institute of Electronics
In this brief, we present a post-deposition annealing technique that employs furnace annealing in N2O (FN2O) to reduce the leakage current of chemical-vapor-deposited tantalum penta-oxide (CVD Ta2O5) thin films, Compared with furnace annealing in O-2 (FO) and rapid thermal annealing in N2O (RTN2O), FN2O annealing proved to have the lowest leakage current and the most reliable time-dependent dielectric breakdown (TDDB).
Smart dielectrics of fluorinated silicon glass prepared by liquid phase deposition method
(2001)
Yeh, CF
;
Chen, TF
;
Lee, YC
;
Liu, CH
;
Lin, SS
Fluorinated silicon glass (FSG) film prepared by using liquid-phase deposition (LPD) is very potential for use as a smart dielectric owing to its high fluorine concentration (8.6 at %), low dielectric constant (3.46), low stress (43 Mpa), low leakage current density (4.6E-9 A/cm(2) at 2 MV/cm) and low deposition temperature (room temperature). By temperature difference and conventional water-adding methods, the LPD technologies and the key process parameters affecting the physicochemical properties and the electrical characteristics will be introduced. Furthermore, the LPD FSG has been applied as gate oxide to MOSFET's and polysilicon TFT's. Owing to its novel property of selective deposition, LPD FSG has been also employed to cap the sidewalls for degradation-free damascene trenches, and to fabricate micro contact holes for the n(+)/p diodes and the Schottky diodes.
Variable-size data item placement for load and storage balancing
(2003-05-15)
Ma, YC
;
Chiu, JC
;
Chen, TF
;
Chung, CP
;
資訊工程學系
The rapid growth of Internet brings the need for a low cost high performance file system. Two objectives are to be pursued in building such a large scale storage system on multiple disks: load balancing and storage minimization. We investigate the optimization problem of placing variable-size data items onto multiple disks with replication to achieve the two objectives. An approximate algorithm, called LSB Placement, is proposed for the optimization problem. The algorithm performs bin packing along with MMPacking to obtain a load balanced placement with near-optimal storage balancing. The key issue in deriving the algorithm is to find the optimal bin capacity for the bin packing to reduce storage cost. We derive the optimal bin capacity and prove that LSB Placement algorithm is asymptotically 1-optimal on storage balancing. That is, when the problem size exceeds certain threshold, the algorithm generates a load balanced placement in which the data sizes allocated on disks are almost balanced. We demonstrate that, for various Web applications, a load balanced placement can be generated with disk capacity not exceeding 10% more than the balanced storage space. This shows that the LSB Placement algorithm is useful in constructing a low cost and high performance storage system. (C) 2002 Elsevier Science Inc. All rights reserved.