Thermal effects in switching of sub-micron tunnel junctions are investigate
d. The switching field is shown to be inversely dependent on temperature, a
nd switching field jitter is shown to be strong function of temperature. Mi
cromagnetic modeling is used to understand thermal effects. In some instanc
es a stability factor (defined as KV/kT) of 100 or more may be required for
acceptable switching field jitter, while with proper optimization of FM la
yers, stability factors of 50 or 60 may suffice.