DC Hot Carrier Reliability at Elevated Temperatures for nMOSFETs Using 0.13μm Technology
| Autor: | Ze-Wei Jhou, 周澤瑋 |
|---|---|
| Rok vydání: | 2005 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 93 Attributed to the increasing scattering during the carriers’ moving, substrate current Ib and hot carrier degradation of MOSFETs are prevalently believed smaller at elevated temperature. However, the degradation of saturation drain current Id,sat at high temperature was reported worse due to the reduction of velocity saturation length, but the degradation of linear drain current Id,lin was still smaller with increasing stress temperature. Other related studies showed that the hot carrier effect existed a transition point (voltage), which reversed the dependence of MOSFETs’ Ib to temperature. This finding was proved with the peak substrate current would reverse its temperature dependence when biased drain voltage Vd across the transition point. These seems consistent findings now facing new challenges as we examine the results of DC hot carrier stress on the nMOSFETs of 0.13 µm technology. In this study, the tested devices were from 0.13 µm technology. The nMOSFETs used in this experiments have Leff = 90 nm with gate oxide thickness of 20Å (Core devices) and Leff = 120 nm with gate oxide thickness of 32Å (I/O devices), all the W = 10 µm. Stress conditions were (1) 25 ℃ (2) 75 ℃ (3) 125 ℃, all at peak substrate current. It is found that the drain currents degradation are not necessary dependent to the Isub. The degradation of the drain currents of I/O devices are found no reverse temperature effect even the stress bias lower than transition point. And the velocity saturation effect may not the main fact to impact the degradation of Id,sat. Comparison with all the drain currents, it is found first time, Id,op is the worst case for designing analog circuits with satisfactory reliability. Although further studies spanning other nodes of technologies and sizes are required, the study at least shows complicated natural of hot carrier effects. Another significant fact revealed here is the substrate current Ib commonly accepted as the statues for monitoring the drain avalanche hot carrier (DAHC) effect is need to be modified since Id degradation and Ib variations versus temperature have different trends. The reason for this may be parts of holes flow to gate oxide through the velocity saturation region as suggested that the combinations of holes and electrons are the main mechanism of DAHC degradation. Therefore the Ib formulation considered all holes of impact ionization flow to substrate may be not reflecting all the facts. However if this problem is intended to be completely solved, the first question needed to fact is how the velocity saturation length is affected by temperature combining drain voltage variations. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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