Shape Memory Alloys and Polymers for MEMS/NEMS Applications: Review on Recent Findings and Challenges in Design, Preparation, and Characterization

Abstract

Rapid progress in material science and nanotechnology has led to the development of the shape memory alloys (SMA) and the shape memory polymers (SMP) based functional multilayered structures that, due to their capability to achieve the properties not feasible by most natural materials, have attracted a significant attention from the scientific community. These shape memory materials can sustain large deformations, which can be recovered once the appropriate value of an external stimulus is applied. Moreover, the SMAs and SMPs can be reprogrammed to meet several desired functional properties. As a result, SMAs and SMPs multilayered structures benefit from the unprecedented physical and material properties such as the shape memory effect, superelasticity, large displacement actuation, changeable mechanical properties, and the high energy density. They hold promises in the design of advanced functional micro- and nano-electro-mechanical systems (MEMS/NEMS). In this review, we discuss the recent understanding and progress in the fields of the SMAs and SMPs. Particular attention will be given to the existing challenges, critical issues, limitations, and achievements in the preparation and characterization of the SMPs and NiTi-based SMAs thin films, and their heterostructures for MEMS/NEMS applications including both experimental and computational approaches. Examples of the recent MEMS/NEMS devices utilizing the unique properties of SMAs and SMPs such as micropumps, microsensors or tunable metamaterial resonators are highlighted. In addition, we also introduce the prospective future research directions in the fields of SMAs and SMPs for the nanotechnology applications.

Wearable Actuators: An Overview

“…With the emerging material science and technology, new smart materials enable the possibility of wearable robots, getting rid of bulky, rigid, and heavy equipment. Thermally driven materials such as shape memory alloys have problems such as high thermal hysteresis, high temperature, and high cost [29]. The actuation force of IPMCs, CNTs and CPs is too small, and it is difficult to make large-scale devices [18].…”

“…As shown in Figure 3, upon heating, phase transformation from martensite to austenite starts at temperature A s and stops at temperature A f , whilst the reverse phase transformation starts at temperature M s and stops at temperature M f during cooling (Figure 3a). There are three major shape memory characteristics for SMAs, namely one-way memory effect, two-way memory effect, and pseudoelasticity [29]. In one-way SMAs, the material is deformed at a low temperature, and the shape can be restored after heating, in which the SME only exists in the heating process.…”

Wearable Actuators: An Overview

“…With the emerging material science and technology, new smart materials enable the possibility of wearable robots getting rid of bulky, rigid, and heavy equipment. Thermally driven materials such as shape memory alloys have problems such as high thermal hysteresis, high temperature, and high cost [29]. The actuation force of IPMCs, CNTs and CPs is too small, and difficult to make large-scale devices [18].…”

“…As shown in Figure 3, upon heating, phase transformation from martensite to austenite starts at temperature As and stops at temperature Af, whilst the reverse phase transformation starts at temperature Ms and stops at temperature Mf during cooling (Figure 3a). There are three major shape memory characteristics for SMAs, namely one-way Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 1 June 2021 doi:10.20944/preprints202106.0035.v1 memory effect, two-way memory effect, and pseudoelasticity [29]. In one-way SMAs, the material is deformed at a low temperature, and the shape can be restored after heating, in which the SME only exists in the heating process.…”

Effect of External Impacts on the Structure and Martensitic Transformation of Rapidly Quenched TiNiCu Alloys

“…Alloys exhibiting shape memory effect (SME) are a bright example of the so-called smart functional materials. The rapid development of these materials in recent decades is caused, on the one hand, by the design of efficient processes of their fabrication and, on the other hand, by their excellent combination of physical and chemical properties which provide their wide application in aviation and space technologies [1,2], power industry and device building [3,4], robot engineering [5,6], MEMS technology [7,8], biomedicine and biotechnology [1,4]. The fabrication of miniaturized and fast operating devices on the basis of SME alloys, in particular for MEMS, requires thin materials with a narrow temperature hysteresis.…”