Comparison of electrical properties of SOS and ISE SOI transistors

Summary form only given. The electrical properties of transistors in SOS and ISE (isolated silicon epitaxy) SOI wafers are compared. The radiation response of transistors fabricated with both types of wafers is included. The improved crystallinity of the ISE material over SOS material was found to affect several key transistor parameters. One was the ON voltage of the body-source diode. The lower ON voltage of the SOS material is a consequence of the higher density of recombination centers. The implication of this effect is that the kink effect and dynamic threshold variation due to gate-to-body capacitive coupling will be larger for ISE N channel transistors than for SOS transistors. For a base current of 10 μA and a gate voltage of -1 V the ISE NFET (L=4 μm) was found to have a beta of 3.5 as compared to the SOS NFET beta of 0.0005. The high beta of the ISE NFET is detrimental to the operation of some common CMOS circuits unless layouts include a body tie to ground. Also, the higher beta of ISE materials lowers BV_dss. The radiation response of transistors indicated comparable threshold shifts. Back-channel leakage was much greater for the ISE NFETs where activation of back-channel leakage occurred at about 100 Krad(SiO₂ )