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Silicon on Insulator Advanced Electronic Devices Karthik Swaminathan
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Reasons for SOI Replacement for SOS Need to extend Moore’s Law Commercial Availability of SOI wafers
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Advantages of SOI Reduced Source and Drain to Substrate Capacitance. Absence of Latchup. Lower Passive current. Denser Layout Low cost.
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SOI Wafer Fabrication Bond and Etch Back SIMOX (Separation by IMplantation Of oXygen) SIMON(Separation by IMplantation Of Nitrogen)
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heat silicon BOX SIMOX
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Fully Depleted (FD) SOI This is what you expect. FDSOI MOSFET Depleted channel. http://www.soisic.com/SOI_keys_benefits.htm
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Partially Depleted (PD) SOI What if active Si layer is thick ? Body in channel floating Floating body effect. http://www.soisic.com/SOI_keys_benefits.htm
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Is SOI just in the textbooks ? 1987IBIS’s commercial SIMOX wafers (3’’ – 6’’) 1988HP’s 2GHz CMOS circuit 1989TI’s commercial 64k SRAM March 2004Apple’s Xserve G5 End 2004AMD 90nm processor
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Novel SOI Devices Dual gate SOI. SOI Single electron transistors.
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Double-Gate SOI MOSFET ITRS roadmap – dual gate SOI at 15nm. Thick gate oxide to ensure equal thickness on both sides. IEEE Tran on Elec. Dev. 50,3,March 2003,Ultimately Thin Double-Gate SOI MOSFETs Thomas Ernst et al.
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Issues – Negative resist for EBL PMMA resist is a good positive resist for EBL. Do we have a good negative EBL resist high resolution. NO alternate techniques.
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Negative Resist – SOI ? EBL. Plasma oxidation. Etching of amorphous silicon. BOX removal.
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Negative resist – silicon ? EBL Plasma oxidation Electron cyclotron resonance chlorine etching of silicon.
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SOI SET
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TEM image of trenches
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AFM image of SET
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Conductance Oscillations Vds = 10mV
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SET by pattern dependent oxidation
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Pattern dependent oxidation
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Thermal gate oxidation. Oxygen diffuses through the BOX and reaches the pattern edges which are oxidized. Stresses due to volume change prevent oxidation of the island.
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Conductance Oscillations Ld=50nm Vds = 1mV
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Conductance Oscillations Ld=70nm Vds = 1mV
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Conductance Oscillations Ld=100nm Vds = 1mV
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Gate capacitance vs Ld
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Summary Future devices will involve SOI. SOI provides certain benefits over bulk CMOS for smaller gate lengths. SOI SETs may become a promising technology in the future.
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