Nondestructive evaluation of large-area PZN-8%PT single crystal wafers for medical ultrasound imaging probe applications

A nondestructive quality evaluation and control procedure for large-area, [001]-cut PZN-8%PT wafers is described. The crystals were grown by the flux technique engineered to promote [001] layer growth of the crystals. The wafers were sliced parallel to the [001] layer growth plane. Curie temperature (T/sub c/) variations, measured with matching arrays of dot electrodes (of 5.0 mm in center-to-center spacing), were found to be better than /spl plusmn/4.01/spl deg/C both within wafers and from wafer to wafer. After selective dicing to give final wafers of narrower T/sub c/ distributions (e.g., /spl plusmn/ 3.0/spl deg/C or better), the wafers were coated with complete electrodes and poled at room temperature at 0.7-0.9 kV/mm. Typical overall properties of the poled wafers were: K/sub 3//sup T/ = 5, 200 (/spl plusmn/10% from wafer to wafer), tan /spl delta/ < 0.01 (all wafers), and k/sub t/ = 0.55 (/spl plusmn/5%) (all percentage variations are in relative percentages). Then, the distributions of K/sub 3//sup S/, tan /spl delta/, and k/sub t/ were measured by the array dot electrode technique. The variations in K/sub 3//sup S/ (hence K/sub 3//sup T/) and k/sub t/ within individual wafers were found to be within 10% and 5%, respectively. The dielectric loss values, measured at 1 kHz, were consistently low, being <0.01 throughout the wafers. The k/sub t/ values determined by the dot electrodes were found to be about 5% smaller than those obtained with the complete electrodes, which can be attributed to an increase in capacitance ratio due to the partial electroding. The k/sub 33/ values, deduced using the relation K/sub 3//sup S/ /spl ap/ (1 k/sub 33//sup 2/) K/sub 3//sup T/, from the mean K/sub 3//sup S/ and overall K/sub 3//sup T/ values, average 0.94 (/spl plusmn/2%). The present work shows that the distribution of T/sub c/ within wafers can be used as a convenient check for the uniformity in composition and electromechanical properties of PZN-8%PT single crystal wafers. Our results show that, to control /spl Delta/K/sub 3//sup T/ and /spl Delta/k/sub t/ within individual wafer to /spl les/ 10% and 5%, respectively, the variation in T/sub c/ within the wafer should be kept within /spl plusmn/3.0/spl deg/C or better.