Fibrous micro-composite materials can be formed from micro fibers and be used to build micro-electro mechanical systems (MEMS) that do not show fatigue after the billions of cycles. The fibrous micro-composite materials are utilized as the basis for a new class of MEMS by Mesmerize. Magnetic, piezoelectric, electrostatic, electrothermal, and electrostrictive responsive fibers are used to form a variety of micro-electro-mechanical devices. In addition to simple fiber composites and microlaminates, fibrous hollow and/or solid braids, can be used in structures where motion and restoring forces result from deflections involving torsion, plate bending and tensioned string or membrane motion. These materials will enable simultaneous high operating frequencies, large amplitude displacements and or rotations, high reliability under cyclical stresses, according to inventor Shahyaan Desai.
Desai is a founder of Mesmerize (Ithaca, NY) which is commercializing MEMS devices from fabricated nanofibers without the use of a matrix material. Fibrous elements are formed using high strength, micron and smaller scale fibers, such as carbon/graphite fibers, carbon nanotubes, fibrous single or multi-ply graphene sheets, or other materials having similar structural configurations. Devices can be built where fibers are attached only at a substrate edge (e.g. cantilevers, bridges). Motions can be controlled by adjusting the linkage between multiple fibers with weak coupling (e.g. base, tip, in-between). Driving mechanisms include base-forcing (magnetics, piezo, electrostatics) or tip forcing (magnetics). Mirrors may be formed on free ends of cantilevers to form optical scanners.
Mezmerize is a designer and manufacturer of micro-electromechanical System (MEMS) mirrors and mirror modules based on a novel carbon fiber materials platform. The unique material properties of carbon fibers permit, for the first time, the development of micro-mirrors that can simultaneously deflect through large angles and reach high scanning speeds. Mezmeriz is currently working with partners to integrate their carbon fiber micro-mirror modules in pico-projectors and laser scanning units for laser printers enabling novel functionality in these devices.
Although MEMS manufacturers have pushed to develop silicon (both polycrystalline and single crystal) and other material-based structures, the resulting systems still lack the needed mechanical properties, according to U.S. Patent 7,616,367 held by Cornell Research Foundation, Inc. (Ithaca, NY). A specific example is the case of MEMS based optical scanners and switches (OMEMS). Such devices need to produce large angular deflections (several tens of degrees) and resonant frequencies exceeding tens of kilohertz with lifetime reliability over billions of cycles.
Monolithic materials, such as silicon, metal and ceramic thin films currently used to produce MEMS lack the required combination of high elastic stiffness, high strength, high fatigue lifetime and low density (mass per unit volume) i.e., the basic mechanical flexibility and flaw tolerance necessary for many potential MEMS applications. Polymers are not adequate since they are too flexible and have low strength which limits them to low frequency operation in devices where low forces and/or displacements are required, such as valves and fluidic pumps.
Consequently, moving component MEMS, such as optical scanners, are nearly non-existent commercially today. Most successful applications of MEMS remain based on quasi-static devices such as pressure and acceleration sensors. One moving component MEMS is a digital light processor that is based on bistable positioning of aluminum MEMS mirrors.
The need for advanced capability MEMS devices can be illustrated through a particular application--the MEMS based optical scanner (an OMEMS). Such scanners are envisioned for large area display applications using three-color scanning. Early MEMS optical scanners utilized a torsional silicon micro-mirror produced using wet etching. It was capable of deflecting a beam through a 0.8.degree. angle at a resonance frequency of 16.3 kHz. The majority of OMEMS scanners in development today are still designed using similar thin beams of silicon acting either as torsion bars (around which a silicon mirror element rotates) or as cantilevers (which vibrate to provide the scanning motion). Both of these structure types are efficient, with no moving parts to wear.
General applications are dependent on the resonance frequency, the maximum deflection, and the maximum restoring force--with higher values of each normally desired. These properties are dependent on the size, shape, and mechanical properties of the underlying materials. However, materials used in traditional IC-based MEMS fabrication lack the mechanical characteristics required to allow specific tailoring and optimization for many applications. There is no current way to design simultaneously for high frequency operation, large amplitude deflection, low operating power, robustness, and long-term reliability under cyclic stresses with existing material systems. The basic problem with silicon, and monolithic materials in general, is that while sufficient elastic stiffness, their strength and fatigue lifetime is too low and density too high. This combination limits the ultimate deflection amplitude and frequency, and increases power requirements to sustain oscillation. having sufficient elastic stiffness, their strength and fatigue lifetime is too low and density too high. This combination limits the ultimate deflection amplitude and frequency, and increases power requirements to sustain oscillation.
Fundamental limitations exist in the performance of materials currently used for MEMS and micro-mechanical devices. These materials such as Si, SiO2, SiC, metals, Si3N4 cannot provide large deflections (>100 um) at high speeds (>kHz) necessary for many MEMS actuator applications hampering their widespread commercialization. Most of all, the existing materials do not have the fatigue life necessary to undergo repeated large deformations over the billions of cycles that most actuator MEMS applications require. Materials developed by Desai overcome may of the problems associated with silicon MEMS devices.
