Abstract: A low energy argon ion beam has been applied to bombard the backsurface of silicon wafers after the ultrahigh frequency low power transistors are fabricated and the noise coefficient of low frequency and high frequency can be decreased effectively the characteristics frequency and current gain of direction current can be increased．The experimental results show that the decreasing of low frequency noise coefficient are relevant to the decreasing of interface state density at SiO2－Si system and the reduction of high frequency is owing to the increasing of the characteristics frequency and current gain of direction current． 

Key words: argon ion, bombardment, noise, lifetime, transistor