Method of estimating lifetime of floating SOI-MOSFET

A method of estimating a lifetime of a floating SOI-MOSFET, comprising the steps of:

• obtaining, corresponding to at least two stress conditions S.sub.1 and S.sub.2, substrate currents Isub.sub.1 and Isub.sub.2, drain currents Id.sub.1.sup.t and Id.sub.2.sup.t and transistor lives .tau..sub.1.sup.t and .tau..sub.2.sup.t for a body-fixed SOI-MOSFET by a hot carrier stress test;
• using at least said Isub.sub.1, Isub.sub.2, Id.sub.1.sup.t, Id.sub.2.sup.t, .tau..sub.1.sup.t and .tau..sub.2.sup.t to determine constants A and B in the following equation (2) ##EQU10## where W.sup.t is a known channel width of said body-fixed SOI-MOSFET;
• obtaining, from measurement, stress condition dependency Isub(S) of the substrate current and stress condition dependency Id.sup.t (S) of the drain current for said body-fixed SOI-MOSFET and obtaining, from measurement, stress condition dependency Id.sup.f (S) of a drain current of said floating SOI-MOSFET;
• and
• using said A, B, Isub(S), Id.sup.t (S) and Id.sup.f (S) to obtain a lifetime .tau.1.sup.f (S) of said floating SOI-MOSFET under an arbitrary hot carrier stress condition from the following equation (5) ##EQU11## where W.sup.f is a known channel width of said floating SOI-MOSFET.