Characterization of laser-induced photoexcitation effect on a surrounding CMOS ring oscillator

The use of laser trimming techniques with conventional CMOS processes requires thorough understanding of the electrical consequences of a laser pulse on surrounding sensitive devices. A study on the laser-induced photoexcitation effect on a ring-oscillator has been performed. Experiments are performed with a laser beam focused on a diffusible resistor made of a n-doped gap between two highly p-doped regions. An in-situ characterization technique has been used to get the laser´s power profile under dielectric layers. A novel frequency-monitoring circuit is presented. It has been manufactured in 0.18 μm CMOS technology and experimental results are presented. It has been measured that the laser causes a 28% change of the oscillating frequency. An approach to model the photoexcitation effect using combined electrical and physical simulations is presented.