RF-SAW filters on pyro-suppressed wafers

The paper describes the problems associated with manufacturing RF-SAW filters on pyroelectric substrates. The presence of the pyroelectric effect on leaky cuts of LiTaO₃ results in manufacturing yield problems for RF-SAWs in the frequency range of 800 MHz to 2.4 GHz. The effect is more significant at higher frequencies (above 2 GHz) where yield fallout from pyroelectric related damage can be as high as 30%. Common layout and metalization techniques used to counter the pyroelectric related damage result in degraded electrical performance and compromise design flexibility. The use of pyro-suppressed LiTaO₃ reduces the yield fallout dramatically. RF L-SAW filters have been fabricated using 42°, 46° and 48° LiTaO₃ with no observable changes in electrical performance or temperature coefficient of frequency. The ideal bulk conductivity range for pyro-suppressed LiTaO₃ needs to be determined. Modeling of pyroelectric charge build up on the metalized die surface can also aid designers in developing device layouts that are less susceptible to pyroelectric related damage.