Over the past 20 years, the channel length of MOS transistors has halved at intervals of approximately every two or three years, which has led to a virtuous circle of increasing packing density (more complex electronic products), increasing performance (higher clock frequencies) and decreasing costs per unit silicon area. To continue on this path, Research is underway at Southampton University to investigate an alternative method of fabricating short-channel MOS transistors, socalled Vertical MOSFET's. In these devices the channel is perpendicular to the wafer surface in stead of in the plane of the surface. Vetical MOSFET's have three main advantages:
- First, the channel length of the vertical MOS transistor is not defined by lithography. This means no requirements for post-optical lithography techniques such as x-ray, extreme ultra-violet, electron projection lithography, ion projection lithography or direct write e-beam which are possibly prohibitively expensive.
Second, Vertical MOS transistors are easily made with both front gate and back gate.
Using this technology doubles the channel width per transistor area. Combined with easier design
rules, this leads to an increase of packing density of at least a factor of four as compared
to horizontal transitors.
One step further, is the use of very narrow pillars with the gate surrounding the entire pillar. This way, fully depleted transistors can be produced which have all the advantages of SOI transistors.
- Third advantage of the vertical MOSFET is the possibility to prevent short channel effects from dominating the transitor by adding processes that are not easily realised in horizontal transistors, such as a polysilicon (or polySiGe) source to reduce parasitic bipolar effects or a dielectric pocket to reduce drain induced barrier lowering (dibl).
Type: Normal Research Project
Research Groups: Nano Research Group, Southampton Nanofabrication Centre
Dates: 1st January 2003 to 1st January 2011
- Reduction of Parasitic Capacitance in Vertical MOSFETs by Spacer Local Oxidation
- Single, double and surround gate vertical MOSFETs with reduced parasitic capacitance
- Self-aligned silicidation of surround gate vertical MOSFETs for low cost RF applications
- University of Liverpool
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