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U. Glaeser

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FIGURE 1.18 Trend of V dd.<br />

FIGURE 1.19 Trend of drain current.<br />

around L g = 30 nm. One small concern is that the I on starts to reduce from L g = 100 nm and could be<br />

smaller than the value specified by the roadmap from L g = 30 nm. This is due to the increase in the S/D<br />

extension resistance in the small gate length MOSFETs. In order to suppress the short-channel effects,<br />

the junction depth of S/D extension needs to be reduced aggressively, resulting in high sheet resistance.<br />

This should be solved by the raised (or elevated) S/D structures. This effect is more significantly observed<br />

in the operation of an 8-nm gate length EJ-MOSFET [20], as shown in Fig. 1.19. In the structure, S/D<br />

extension consists of inversion layer created by high positive bias applied on a 2nd gate electrode, which is<br />

placed to cover the 8-nm, 1st gate electrode and S/D extension area. Thus, reduction of S/D extension<br />

resistance will be another limiting factor of CMOS downsizing, which will come next to the limit in thinning<br />

the gate SiO 2.<br />

In any case, it seems at this moment that SiO 2 gate insulator could be used until the sub-1 nm thickness<br />

with sufficient MOSFET performance. There was a concern proposed in 1998 that TDDB (Time Dependent<br />

Dielectric Breakdown) will limit the SiO 2 gate insulator reduction at t ox = 2.2 nm [21]; however,<br />

recent results suggest that TDDB would be OK until t ox = 1.5 − 1.0 nm [22–25]. Thus, SiO 2 gate insulator<br />

would be used until the 30 nm gate length generation for high-speed MPUs. This is a big change<br />

© 2002 by CRC Press LLC<br />

Id (mA/ m)<br />

µ<br />

V dd (V)<br />

10 0<br />

10 −1<br />

10 −2<br />

10 1<br />

10 0<br />

Lg ( m)<br />

8 6 2 1 0.1 0.03<br />

Intel<br />

(Tox : 2 nm)<br />

Intel (plan)<br />

µ<br />

Toshiba<br />

(Tox : 1.5 nm)<br />

Lucent<br />

(Tox: 1.3 nm)<br />

10−<br />

Year<br />

1<br />

Intel<br />

(Tox : 0.8 nm)<br />

1970 1980 1990 2000 2010 2020<br />

Lg ( m)<br />

8 6 2 1 0.1 0.04 0.03<br />

Intel’99<br />

(IEDM99)<br />

Toshiba’94<br />

(IEDM94)<br />

Lucent’99<br />

(IEDM99)<br />

IBM’99 (SOI)<br />

Toshiba’93<br />

(IEDM99)<br />

(IEDM93)<br />

Intel’00<br />

(IEDM00)<br />

Intel 2000 (plan)<br />

ITRS (I on )<br />

ITRS’99 (plan)<br />

NEC’99 (EJ-MOSFET)<br />

(SSDM99)<br />

: with ITRS scaling parameters<br />

: thicker gate insulator than ITRS<br />

1970 1980 1990 2000 2010 2020<br />

Year<br />

µ<br />

0.008<br />

2030

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