Cellulose Smart Material for Sensor, Actuator and MEMS Applications

Cellulose Electro-Active Paper (EAPap) has been discovered as a smart material that can be used as a sensor and actuator [1]. It has many advantages in terms of low voltage operation, light weight, low power consumption, low cost, biocompatibility and biodegradability. EAPap is made with cellulose paper coated with thin electrodes. EAPap shows a reversible and reproducible bending movement as well as longitudinal displacement under electric field. The out-of-plane bending deformation is useful for achieving flapping wings, micro-insect robots, and smart wall papers. On the other hand, in-plane strains, such as extension and contraction of EAPap materials are also promising for artificial muscle applications. The actuation principle of cellulose EAPap bending actuator is known to be a combination of piezoelectric effect and ion migration effect. This paper presents further investigation of cellulose EAPap for actuator, sensor and MEMS devices. Piezoelectricity is one of major actuating mechanism of cellulose EAPap. Cellulose is a complex anisotropic material. Aligning cellulose fibers in the fabrication process is a critical parameter to improve mechanical and electromechanical properties of EAPap such as stiffness, strength, piezoelectricity and so on. Cotton cellulose fibers are dissolved into a solution using NaOH/urea and DMAc/LiCl methods. In the later method, the dissolution and shaping of cellulose can be carried out by DMAc/LiCl. Cellulose pulp was mixed with lithium chloride (LiCl) and dehydrated by heating. After adding DMAc (N, N-dimethylacetamide) to the mixture, swell it in room temperature. By heating it a solution formation can be obtained. There are some issues on eliminating solvent and ions and regenerating a pure cellulose films. The material processing all about EAPap has been introduced [2, 3]. Wet drawn stretching method is used in the fabrication process of cellulose film to increase its mechanical and electromechanical properties. This wet-drawn cellulose EAPap is termed as Piezo-Paper. Cellulose EAPap material can be customized to satisfy the material requirement for specific applications. Piezo-Paper can be used for strain sensors, vibration sensors, ultrasonic transducers, SAW devices, speakers, microphones, stack actuators, bending actuators and MEMS devices. Figure 1 shows some applications. Piezoelectric charge constant of Piezo-Paper is 70 pC/N. Details of piezoelectric characteristics of Piezo-Paper and its applications are presented in this paper. Micro-fabrication on cellulose EAPap has many applications, for example, MEMS sensors, e-Paper, thin film transistor (TFT), and even microwave-driven EAPap actuator. To develop microwave-driven EAPap actuator, rectenna (rectifying antenna) has been developed [4]. Rectenna can rectify microwaves and feed dc power without wire. Thus, this technology has many applications. To fabricate the rectenna array on cellulose EAPap, micro patterning of metallic layer and Schottky diode fabrication were studied. The Schottky diode fabrication gives the possibility of TFT on cellulose sheet. Advancing from this technology, SAW (Surface Acoustic Wave) device fabrication for humidity sensor is possible. The devices fabrication along with the characterization and their demonstration will be shown. Cellulose EAPap technology will bring the dream of flying magic paper into real world in the near future.