Semiconductor devices are used in a large number of electronic devices, such as computers, cell phones and others. One of the goals of the semiconductor industry is to continue shrinking the size and increasing the speed of individual devices. Every generation of semiconductor devices is smaller than the previous generation by about 50%, thus reducing the cost per device significantly.
A key challenge in scaling semiconductor devices arises due to the increase in leakage currents at short channel lengths. Halo implants are used to mitigate this increase leakage arising from short channel effects. However, use of halo implants increases the channel doping as well counter-dopes the source and drain junctions. Both these effects increase the effective resistance of the transistor. However, short channel devices compensate some of this loss by gate length scaling accompanying the technology development. However, longer gate length transistors built on such short channel device technologies do not enjoy this advantage and are hence degraded. This is often not a problem in digital technologies that use only the short gate length devices.
Analog circuits typically employ longer gate length devices and cannot take advantage of these aggressively scaled transistors. For example, these short channel digital devices have lower analog intrinsic gain as well as increased gate leakages. Due to cost constraints, analog technologies utilize the CMOS technologies developed for digital applications. As the long gate lengths devices are also degraded, many analog applications require individually tailored technology flows, considerably increasing production costs.
Hence, improved methods, structures of forming and designing analog devices are needed that are compatible with existing CMOS technologies.
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