A Thin-Film Piezoelectric Speaker Based On An Active Microstructure Array

We report a thin-film acoustic speaker based on the actuation of a dense array of freestanding piezoelectric microstructures. The microstructure array is embossed on an ultra-thin polyvinylidene fluoride (PVDF) film in a self-aligned manner using vacuum and thermal treatments, and is also protected by a perforated passive layer on top. A 100 cm² thin-film speaker (81 cm² active area) achieves 75 dB sound pressure level (SPL) at 5 kHz and 50 cm distance using 20 V excitation. Its frequency response does not roll off below 100 kHz, owing to the microstructure design. Our speaker can be mounted on various surfaces, thereby rendering the surfaces acoustically active with high sensitivity at both audible and ultrasonic frequencies, which enables broader application prospects over prior PVDF speakers based on freestanding and curved designs. The simple structure, the uniform performance, and the scalable low-cost fabrication of our speaker constitute significant advantages over cellular-electret speakers for large-scale application. Therefore, this thin-film speaker could perform as a new acoustic platform for active noise control, robotics, and virtual/augmented reality.

Introduction

The emerging internet of things, artificial intelligence, robotics and virtual/augmented reality have created a demand for widely-deployed acoustic interfaces. Thin-film loudspeakers based on polymers with intrinsic or artificial piezoelectricity are gaining attention in such applications as a result of their light weight, flexibility, scalability, nonintrusive installation, and low-cost, high-throughput fabrication [1], [2]. Thus, they offer significant advantages over commercial dynamic loudspeakers and other candidate technologies [3], [4]. They can also be used as wallpaper to create surround-audio and thus provide an immersive experience for virtual/augmented reality, or mounted on vehicle or aircraft interiors to achieve active noise control [5], [6]. The prior art of thin-film loudspeakers requires either freestanding and curved PVDF sheets [2], [7] or cellular electrets with charged voids [8], [9]. The former design limits the applications of PVDF speakers, while the scalable fabrication of cellular electrets faces challenges due to their complicated structure, nonuniformity in characteristics, and device instability. Therefore, a high-performance thin-film speaker suitable for large-area application in broad scenarios is in acute need.