1. Channel Shape Effects on Device Instability of Amorphous Indium-Gallium-Zinc-Oxide FETs
Seung Jae Yu, Jae Hyun Ryu, Geun Woo Baek,
Jong Hun Hong and Sung Hun Jin*
Department of Electronic Engineering,
Incheon National University

2. I II III IV Outlines Introduction (Motivation) Experimental details
Asymmetry Effects on S/D Electrodes
Vertical Field Effects on Reliability
Lateral Field Effects on Reliability
III
Results and discussion IV
Summary

3. a-IGZO TFTs: Advantages vs. Constraints
Advantage of IGZO TFTs
Key Limitation
Device Reliabilities Issues
Bias temperature stress
Light induced degradation
Local field effects
Channel shape (Cgs)
VGS(V)
IDS(mA)
Reliability issues for a-IGZO TFTs are not fully resolved yet.

4. For Stable Applications,
Hojin Lee, et al, J.J.APL, 50 (2011)
TFT parasitic capacitance  Kick-back voltage
U-type is popular due to the low Cgs of TFTs with the same W/L
Importance of channel shape
 Localized field, Cgs (kick back voltage)

5. For stable Applications,
Importance of channel shape
Localized field induced degradation
Few study has been reported, but still important.

6. ZIGZAG Circular U-type
Comparative Study Depending on Channel Shape
Gate
ZIGZAG
Drain
Source
Gate
Circular
Drain
Source
Drain
Source
Gate
U-type
Bottom gate structure
Same channel width and length
 W/L=100/4 m

7. Device Geometry for a-IGZO TFTs
glass
IGZO
SiNx/SiOx
SiOx
Gate
SiNx/SiOx=400 nm/50 nm
Inverted staggered bottom gate structures

8. I II III IV Outlines Introduction (Motivation) Experimental details
Asymmetry Effects on S/D Electrodes
Vertical Field Effects on Reliability
Lateral Field Effects on Reliability
III
Results and discussion IV
Summary

9. Experimental results (Original, S/D Change)
Possible reasons for observed behaviors:
S/D asymmetry effects are negligibly observed.
Transfer length(LT) is large enough compared with the width of gate electrodes.
Full gate structures for a-IGZO TFTs
Hojin Lee, et al, J.J.APL, 50 (2011)

10. Experimental results (Original, S/D Change)
Possible reasons for observed behaviors:
S/D asymmetry effects are negligibly observed.
Transfer length(LT) is large enough compared with the width of gate electrodes.
Full gate structures for a-IGZO TFTs
Hojin Lee, et al, J.J.APL, 50 (2011)

11. I II III IV Outlines Introduction (Motivation) Experimental details
Asymmetry Effects on S/D Electrodes
Vertical Field Effects on Reliability
Lateral Field Effects on Reliability
III
Results and discussion IV
Summary

12. Vertical E-field Effects (VDS=0.1V, VGS=25V)
Only vertical e-field effects
VGS=25V, E=1.2 MV/cm
Only charge trapping in the channel

13. Experimental results (VD=0.1V, VGS=25V)
𝑽 𝒕𝒉 = ∆𝑽 𝒕𝒉 𝟏−𝒆𝒙𝒑 −( 𝒕 𝝉) 𝜷
circular
U-type
zigzag 𝜷
0.244
0.246
0.256 𝝉
7.87
8.59
7.71
→ Negligible error rate, 10%↓
Only vertical e-field effects, VGS=25V, E=1.2 MV/cm
Jeong-Min Lee1*, et al, Applied Physics Letters 93, (2008);

14. I II III IV Outlines Introduction (Motivation) Experimental details
Asymmetry Effects on S/D Electrodes
Vertical Field Effects on Reliability
Lateral Field Effects on Reliability
III
Results and discussion IV
Summary

15. Lateral E-field Effects (VGS=VDS=5V; Saturation)

16. Lateral E-field Effects (VGS=VDS=10V; Saturation)

17. Experimental results (VDS=VGS=5V)
𝑽 𝒕𝒉 = ∆𝑽 𝒕𝒉 𝟏−𝒆𝒙𝒑 −( 𝒕 𝝉) 𝜷
circular
U-type
zigzag 𝜷
6.04
5.84
7.57 𝝉
0.531
0.544
0.328
Jeong-Min Lee1*, et al, Applied Physics Letters 93, (2008);

18. Experimental results (VDS=VGS=10V)
𝑽 𝒕𝒉 = ∆𝑽 𝒕𝒉 𝟏−𝒆𝒙𝒑 −( 𝒕 𝝉) 𝜷
circular
U-type
zigzag 𝜷
0.66
0.65
0.64 𝝉
3.14
3.64
3.07
Jeong-Min Lee1*, et al, Applied Physics Letters 93, (2008);

19. Lateral E-field Effects (VGS=VDS=15V; Saturation)
Vth = 1.5V (zig-zag)
Vth = 0.65V (circular, U-type)

20. Experimental results (VDS=VGS=15V)
𝑽 𝒕𝒉 = ∆𝑽 𝒕𝒉 𝟏−𝒆𝒙𝒑 −( 𝒕 𝝉) 𝜷
circular
U-type
zigzag 𝜷
0.64
0.48
0.3 𝝉
2.83
3.26
10.42
Lateral e-field: E=15V/4um=3.8 MV/m=0.038 MV/cm
S.M. Sze, Physics of Semiconductor device, p.402

21. Field Conversion Factors
𝜸=𝜷𝑾
𝜸:𝐞𝐟𝐟𝐞𝐜𝐭𝐢𝐯𝐞 𝐟𝐢𝐞𝐥𝐝 𝐞𝐧𝐡𝐚𝐧𝐜𝐞𝐦𝐞𝐧𝐭 𝐟𝐚𝐜𝐭𝐨𝐫
𝜷: 𝒄𝒐𝒏𝒗𝒆𝒓𝒔𝒊𝒐𝒏 factor
Field conversion factors (relative permittivity (a-IGZO=16)
Lateral e-field: E=0.3 MV/cm (Si avalanche breakdown)
Lateral e-field: E=15V/4um=3.8 MV/m=0.038 MV/cm