Stability of Amorphous Silicon Thin Film Transistors under Prolonged High Compressive Strain

AbstractWe studied the effect of prolonged mechanical strain on the electrical characteristics of thin-film transistors of hydrogenated amorphous silicon made at a process temperature of 150°C on 51-μm thick Kapton polyimide foil substrates. Effects are observed only at very high compressive strain of 1.8%. Tensile strain up to fracture at 0.3% to 0.5% does not show any effect, nor does compressive strain substantially less than 1.8%. The TFTs were stressed for times up to 23 days by bending around a tube with axis perpendicular to the channel length, and were evaluated in the flattened state. The changes observed are small. The threshold voltage is increased, the “on” current and the field effect mobility remain essentially constant, and the subthreshold slope, “off” current and gate leakage current drop somewhat. Overall, the observed changes are small. We conclude that mechanical strain caused by roll-to-roll processing and permanent shaping will have negligible effects on TFT performance.

Download Full-text

Effects of Mechanical Strain on the Electrical Performance of Amorphous Silicon Thin-Film Transistors with a New Gate Dielectric

MRS Proceedings ◽

10.1557/proc-1196-c02-02 ◽

2009 ◽

Vol 1196 ◽

Author(s):

Katherine Wei Song ◽

Lin Han ◽

Sigurd Wagner ◽

Prashant Mandlik

Keyword(s):

Thin Film ◽

Amorphous Silicon ◽

Hybrid Material ◽

Thin Film Transistors ◽

Gate Dielectric ◽

Compressive Strain ◽

Mechanical Strain ◽

Electrical Performance ◽

Silicon Thin Film ◽

Transfer Characteristics

AbstractThe stiff SiNx gate dielectric in conventional amorphous silicon thin film transistors (TFTs) limits their flexibility by brittle fracture when in tension. We report the effect on the overall flexibility of TFTs of replacing the brittle SiNx gate dielectric with a new, resilient SiO2-silicone hybrid material, which is deposited by plasma enhanced chemical vapor deposition. Individual TFTs on a 50μm-thick polyimide foil were bent to known radii, and measurement of transfer characteristics were made both during strain and after re-flattening. Compared with conventional TFTs made with SiNx, TFTs made with the new hybrid material demonstrated similar flexibility when strained in compression and significantly increased flexibility when strained in tension. Under bending to compressive strain, all TFTs tested delaminated from the substrate for compressive strains greater than 2%. Conventional a-Si:H/SiNx TFTs have been previously found to delaminate at a similar compressive strain. Under bending to tensile strain, the most flexible TFTs made with the new hybrid material that were tested after re-flattening did not exhibit significant changes in transfer characteristics up to strains of ∼2.5%. Conventional a-Si:H/SiNx TFTs have been found to remain functional for strains of up to 0.5%, a value only one-fifth of that for TFTs made with the new hybrid material.

Download Full-text

Effects of Top Insulator Overlap on the Stability in Hydrogenated Amorphous Silicon Thin Film Transistors

MRS Proceedings ◽

10.1557/proc-336-793 ◽

1994 ◽

Vol 336 ◽

Author(s):

H.S. Choi ◽

Y.S. Kim ◽

S.K. Lee ◽

J.K. Yoon ◽

W.S. Park ◽

...

Keyword(s):

Thin Film ◽

Amorphous Silicon ◽

Thin Film Transistors ◽

Hydrogenated Amorphous Silicon ◽

Charge Trapping ◽

Channel Length ◽

Gate Insulator ◽

Silicon Thin Film ◽

Bias Stress ◽

Hydrogenated Amorphous

ABSTRACTThe effects of top-insulator on the instability problems of hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) have been studied. In a-Si:H TFT with top-insulator (E/S type), charge trapping into the both of top-insulator and gate insulator has been shown under the bias stress.In order to investigate the charge trapping effects of top-insulator, we proposed a new method of Measurement. By this Method, we observed that trapped charges in top-insulator increased drain currents for positive gate bias stress, and this increment of drain currents was more serious with increasing the ratio of source/drain overlap length to channel length. It has founded that the instability problems of a-Si:H TFTs was attributed to the effects of top-insulator as well as that of gate insulator.

Download Full-text

Electrode Interdependence and Hole Capacitance in the Capacitance -Voltage Characteristics of Hydrogenated Amorphous Silicon Thin-Film Transistors

MRS Proceedings ◽

10.1557/proc-507-67 ◽

1998 ◽

Vol 507 ◽

Author(s):

Hyuk-Ryeol Park ◽

J. David Cohen

Keyword(s):

Thin Film ◽

Amorphous Silicon ◽

Thin Film Transistors ◽

Hydrogenated Amorphous Silicon ◽

Channel Length ◽

Silicon Thin Film ◽

Low Frequencies ◽

Capacitance Voltage ◽

Electrode Capacitance ◽

Hydrogenated Amorphous

ABSTRACTThe inter-electrode capacitance - voltage (C-V) characteristics of back-channel etched inverted-staggered hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) were investigated. It is demonstrated that this simple measurement can be used to diagnose TFT parameters such as the fabricated channel length, the channel resistance, and the error in the mask alignment of the source and drain overlap lengths. The C-V characteristics associated with the hole accumulation in a-Si:H TFTs with n+-type source/drain contacts were also examined. We observed that the a.c. capacitance increases for low frequencies and/or moderately high measurement temperatures provided the gate voltage is sufficiently negative.

Download Full-text