Rapid Prototyping of Microactuators by Integrating 3D Printed Polymeric Structures with NiTi Thin Film

This work demonstrates the first sputtered thin-film nickel-titanium (NiTi) shape-memory alloy (SMA) actuators combined with direct 3D printing of polymeric structures. Resulting actuators are fast to prototype, reliable and stable (up to 5000 cycles), and can utilize complex geometries challenging to achieve with conventional MEMS microfabrication. The actuator design uses 3D printed polymer as the passive layer in unimorph actuators, adding significant versatility to the actuator design. An actuator designed for high force-displacement was fabricated with a 15 μm thick polymer layer and characterized by applying currents up to 18 ma (7.3 mW, producing ~156°C) resulting in a maximum displacement of 3.3 μm and ~0.9 mN blocking force. Dynamic operation with falling/rising times of 20.1 ms/9.8 ms and 33.5 Hz maximum operation frequency was also demonstrated.

Introduction

The need for high work density actuators with low power consumption is important for modern MEMS and microrobotic applications [1]. Shape memory alloys (SMA) are particularly compelling because of their high inherent work density (∼1 J/g) and past use in microfabrication [2]–[4]. SMA is also attractive at the MEMS scale because it enables passive actuation with laser irradiation [5], and recently has been demonstrated using lowered crystallization temperatures to facilitate integration with CMOS and soft polymeric materials [6]. Recent developments in SMA actuators reduced the power consumption and increased frequency by using thin co-sputtered NiTi layers with 2D-patterned photoresist layers and simple geometries [6]. The goal of this work is to further enhance the functionality of thin film SMA actuators through integration with 3D printed polymeric structures.