Thin Film Transistors (TFTs)

The a-Si:H TFT is critical to today’s large area, high performance LCDs as well as for many large area microelectronics. The poly-Si TFT has been proved to be an effective loading device in SRAM. It has many potentials in LCD and other high speed (compared with a-Si:H TFT) applications. We study both types of TFTs from different angles. Recently, we invented and studied a new type of a-Si:H TFT nonvolatile memory, which greatly expands the application of the low-temperature prepared transistor to new territories.

a-Si:H TFTs

Plasma enhanced chemical vapor deposition (PECVD) is the only practical large area, low temperature, high throughput fabrication method for a-Si:H TFT arrays today. Although a-Si:H TFTs function adequately for LCD as well as many new microelectronic and opto-electronic applications, the performance is usually below the practical limit due to the poor understanding of many process, thin film materials, and device issues. The a-Si:H/gate SiNx interface chemical and physical properties are especially critical to the TFT characteristics. Previously, we have carried out various studies on this subject. The results can be found in the Publications List. Currently, we are exploring applications of a-Si:H TFTs to novel electronic areas.

The following are examples of some topics that we have studied:

a-Si:H TFT Nonvolatile Memories

 

 

 

 

Y. Kuo and H. Nominanda, APL 89, 173503 (2006).

H. Nominanda and Y. Kuo, ECS Trans. 3, (8) 333 (2006).

 

 

Floating-Gate a-Si:H MIS Capacitors

 

                            

 

H. Helinda and Y. Kuo, ESL 10(8), H232-234 (2007)

Y. Kuo and H. Nominanda, MRS Proc. 2007.

 

 

Bipolar TFT

Y. Kuo, Darpa Macroelectronics Workshop, 11/06/03.

 

Y. Kuo, R. Lei, etc., ECS TFTT VII Symp., 2004.

P-channel TFT

Y. Kuo, Darpa Macroelectronics Workshop, 11/06/03.

Y. Kuo et al., ECS TFTT VI proc, 2002.

TFT with RIE’d Copper Interconnection

A complete a-Si:H TFT with the source and drain regions composed of copper and molybdenum.

ESCA of Hydrogen Plasma Exposed SiNx Surfaces

Y. Kuo, S. Lee, S. Lee, J. P. Donnelly, J.-Y. Tewg, and H. H. Lee.
Electrochem. Soc. TFTT V Symp. Proceedings, PV 2000-31, 34-39, 2001.

Interface Engineering of TFT

ESCA of Hydrogen Plasma Exposed SiNx Surfaces

Y. Kuo. Vacuum, 59, 484-491, 1999.

Novel Structures

Horizontally redundant, vertically redundant, multi-channel single gate, etc.

Self-aligned, 2-photomask, Tri-Layer TFT Structure and Processes

 

Y. Kuo, JECS, 138(2), 637, 1991.
Semiconductor International, Industry News, p. 22, June 1992.

Graded SiNx Gate Dielectric TFT

 

Y. Kuo, JECS, 141(4), 1061, 1994.

Multi-step a-Si:H Deposition for TFT

 

Mobilities of Multi-step Deposited a-Si:H TFTs

Y. Kuo. APL 67(15), 2173. 1995.

Unified gate SiNx RI to Vth relation


Y. Kuo, JECS 142(1), 186, 1995.

Process Induced Damages and TFT Reliability

Y. Kuo, ECS TFTT IV Symp., 192, 1998.

 

Poly-Si TFTs

The poly-Si TFT has a much higher mobility than the a-Si:H TFT has. This enables the circuit designers to add many new functions into the product. However, before the poly-Si TFT is acceptable for large-area, mass production, its process conditions have to be compatible with the low temperature substrate. Recently, we published a pulsed rapid thermal annealing (PRTA) process. When this process is combined with the metal contact structure, poly-Si can be formed at a high rate, e.g., > 10 micrometers per 1-second pulse, with a low thermal budget. This method has no limit on the substrate size. This technology can be used to fabricate not only the large area poly-Si TFT array but also the shallow junction VLSI devices. Since this is a new technology, there are many unknown material and process issues. We are examining these fundamental issues with the goal of fabricating advanced devices. Some of the results are shown below. For more detailed information, please see the Publications List.

Pulsed Rapid Thermal Annealing (PRTA)

 

 

 

Y. Kuo and P. Kozlowski, APL 69(8), 1091, 1996; Y. Kuo, ECS TFTT III, 96-23, 30, 1996.

 

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