There is growing interest in integrating piezoelectric materials with complementary metal-oxide-semiconductor (CMOS) technology to enable expanded applications. A promising material for ultrasound transducer applications is poly(vinylidene fluoride) (PVDF), a piezoelectric polymer. One of the challenges with PVDF is that its piezoelectric properties can deteriorate when exposed to temperatures in excess of 70 °C for extended periods of time during fabrication. Here, we report on the effects of both shortening annealing times and providing this heating nonuniformly, as is characteristic of some processing conditions, on the piezoelectric coefficient (d₃₃) of PVDF films for various thicknesses. In this case, no degradation in the d₃₃ was observed at temperatures below 100 °C for anneal times of under 1 min when this heating is applied through one side of the film, making PVDF compatible with many bonding and photolithographic processing steps required for CMOS integration. More surprisingly, for one-sided heating to temperatures between 90 and 110 °C, we observed a transient enhancement of the d₃₃ by nearly 40% that lasted for several hours after these anneals. We attribute this effect to induced strain in these films.

中文翻译：

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预极化聚偏二氟乙烯薄膜压电响应的温度依赖性

人们越来越关注将压电材料与互补金属氧化物半导体 (CMOS) 技术集成以实现扩展应用。一种用于超声换能器应用的有前途的材料是聚偏二氟乙烯 (PVDF)，一种压电聚合物。PVDF 的挑战之一是，在制造过程中长时间暴露在超过 70°C 的温度下时，其压电性能会恶化。在这里，我们报告了缩短退火时间和不均匀加热对不同厚度的 PVDF 薄膜的压电系数 ( d ₃₃ )的影响，这是某些加工条件的特征。在这种情况下，d ₃₃没有退化当通过薄膜的一侧施加这种加热时，在低于 100°C 的温度下观察到退火时间不到 1 分钟，使 PVDF 与 CMOS 集成所需的许多键合和光刻工艺步骤兼容。更令人惊讶的是，对于单侧加热到 90 到 110 °C 之间的温度，我们观察到d ₃₃的瞬时增强近 40%，并在这些退火后持续了几个小时。我们将这种效应归因于这些薄膜中的诱导应变。