microelectronics technology
To realize high performing devices, it is essential to not only have high channel
mobility, but also good “on/off” switching characteristics. Turning the device from its “on” to “off” configuration causes a shift in the channel energy level from a position close to the band edge (conduction band for n-FET,and valence band for p-FET) towards the mid-gap. Efficient swing of the channel potential by the gate bias requires a low level of interface traps in the range of interest
free carriers (holes) can be collected in the p-channel. Similarly, the low density of interface traps levels near the InGaAs conduction band edge means less acceptor-like traps and more free electrons for forming the n-channel.
Such features are encouraging. Not only do they make transistor operation possible - they allow the high carrier mobility nature of the germanium p-MOSFET and InGaAs n-MOSFET to be unleashed.
To verify this promise, we have fabricated inversion-type
surface-channel MOS transistors with 8 nm of Al2O3 on both germanium substrates with n-type doping of
3 x 1016 cm-3, and In0.53Ga0.47As substrates with p- type doping of 1 x 1017 cm-3. These have been produced with exactly the same oxide stack process that we have already described.
These self-aligned germanium and InGaAs MOSFETs that are built with common gate stack design have produced a very encouraging set of results. These include drain currents of 600 mA/mm and 200 mA/mm at a 2.5 V gate bias swing for InGaAs and germanium MOSFETs respectively. Both transistors have a gate length of 1.5 µm (see Figure 4).
The mobilities in the channels of our common gate stack MOSFETs with 10 µm gates are comparable to the best- reported values anywhere: Hole and electron field-effect mobility values are 400cm2/V-s and 1300cm2/V-s, respectively. Producing these results with the common gate stack is a very important breakthrough for the future of alternative CMOS architectures, because it shows that this approach has the potential to draw on the strengths of III-Vs and germanium.
Further reading J. Mitard et al., IEDM Tech. Dig., 873 (2008) Y. Xuan et al., IEDM Tech. Dig., 371 (2008) G. Dewey et al., IEDM Tech. Dig., 487 (2009) M. Radosavljevic et al., IEDM Tech. Dig., 319 (2009)
Figure 4: imec’s InGaAs and germanium FETs show promising drain currents and mobilities that are comparable to the best results realized anywhere
D. Nguyen et al., ECS Trans., 27 959 (2010) M. Wistey et al., ECS Trans., 19, 36, (2009) D. Lin et al., IEDM Tech. Dig., 327 (2009)
July 2010
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