Remotely Controlled Microscale 3D Self‐Assembly Using Microwave Energy

Abstract

for self-assembly. The heat energy is usually applied from an external source, such as a hotplate [51] or hot liquid bath, [52][53][54][55] which requires direct contact with the heat source. Another way to induce changes in the physical/chemical property is to apply environmental (e.g., pH or ionic strinength) changes to solvent-sensitive hinge materials. [20,56,57] Physical/chemical reactions occur when solvents are in contact with the hinge materials, triggering the self-assembly. However, a major drawback of these assemblies is that the direct contact of heat energy sources or chemicals with the hinge materials critically limits its applications and reduces the manipulative capability of the selfassembly because the heat sources are not controllable, and the environment around the microstructures is not accessible in many practical situations. Moreover, direct heat energy sources, such as a hotplate or a hot liquid bath, usually have a high thermal mass, leading to a thermal lag (or time delay) from when the input energy is controlled to when the 2D structures begin to assemble. Thus, the assembling process cannot be precisely controlled using such methods.Recently, remote-controlled self-assembly has been developed using microwave energy to avoid direct contact between heat sources and structures and to achieve precise control of self-folding. [58] The microwave energy causes the temperature of the millimeter-scale hinge materials (i.e., graphene ink and metal nanoparticles) to increase and trigger self-folding. The remotely applied microwave energy leads to quickly and accurately controlled folding of polymer sheets, which are ideal for time sensitive applications and remotely controlled applications. However, the advanced self-assembly technique using microwave energy needs to be further investigated in order to create 3D self-assembled structures for various applications, including 3D sensors, carriers, and microbots. Also, the ability to build 3D structures on a microscale is necessary because microscale self-assembly allows for the realization of 3D structures that can be used for diverse 3D terahertz sensors [54] and biomedical devices designed for in vivo operation. [10][11][12]56,57] In addition, the development of complex 3D microstructures and microbots requires self-assembly having the ability to conduct different configurations (controllable multiple folding angles of each frame) simultaneously during a self-assembly process. Multiple configurations can be achieved under uniform stimulation by applying different hinge materials, [59] using angle-lock A novel, remotely controlled assembly process is developed to create microscale, self-assembled 3D structures using remote-controlled microwave energy. A nanometer thick chromium (Cr) film absorbs electromagnetic microwaves and generates heat energy, which induces reflow of polymeric hinges. This leads to self-assembly of microscale 3D cubic structures. Since this assembly process does not require direct contact with a heat source or chemicals, micro...

3D Self‐Assembled Microelectronic Devices: Concepts, Materials, Applications

“…[31,61,62] By applying extrinsic forces, structural buckling was studied in detail to form diverse pop-up 3D architectures. [31,[63][64][65] Intrinsic interfacial [66][67][68][69][70][71] or volumetric stresses [14,[72][73][74][75][76] were successfully used to create rolled-up tubular and "Swiss-roll" architectures. In their deployed state, these essentially reshaped 2D membranes with thicknesses from nano-to micrometers experience fully integrated electronic functionalities as there is direct compatibility between shapeable materials technologies and conventional thin-film microfabrication processes.…”

Self‐Folding Using Capillary Forces

“…Capillary self-folding with multiple panels can also be used to assemble electromagnetic devices and antennas that are omnidirectional and enable sensing or detection with angular information. [162][163][164][165] For example, by patterning functional sensing elements on all faces of a cube, it was possible to sense chemicals deposited at multiple angles. [166,167] One of the challenges in the miniaturization of wireless electronic devices is to minimize the size of antennas without compromising the radiation efficiency for applications such as in bioimplants or smart dust.…”

Small‐Scale Biological and Artificial Multidimensional Sensors for 3D Sensing

“…The surface‐tension‐driven self‐assembly approach is a versatile process that can be easily scaled and programmed for desired applications. The heat energy required for melting the polymer hinge can be provided through ion beams, magnetic fields, microwaves, or hot plates . Thus, enabling its application in an in‐vivo biological environment, long range remote assembly, and in‐situ monitored programmable self‐folding for achieving precisely controlled 3D micro‐ and nanostructures.…”

“…Another limiting factor in the development of these 3D optical sensors has been the use of the low melting point metallic hinge material for the self‐folding mechanism which can cause distortion in the frequency spectrum . However, a new folding mechanism introduced the use of polymer based hinges which triggered assembly of the 2D pattern into 3D structures when heated to 60–100 °C . The resulting transmission spectrum (Figure e) is free of any distortions and contains three clear, sharp peaks corresponding to the resonator of each length, where the amplitude of the peaks changes in response to rotation of the sensor.…”