Abstract
We are reporting on the fabrication and characterization of microscale electromechanical actuators driven by the internal forces induced within the depletion region of a typical pn junction. Depletion region actuators operate based on the modulation of the interactions of the internal electric field and the net space charge within the depletion region of a pn junction by an external potential. In terms of performance, depletion region actuators fall between electrostatic actuators, where a physical gap separates the charges on two electrodes, and piezoelectric actuators, where the separation between the charges is on the order of lattice constants of the material. An analytic model of depletion region actuator response to an applied potential is developed and verified experimentally. The prototype micro-mechanical device utilized the local stresses produced by the depletion region actuators to generate mechanical vibrations at frequencies far below the resonance frequencies of the structure. A laser Doppler vibrometer was used to measure and compare the displacements and vibration patterns caused by the depletion region and electrostatic actuators. Utilizing depletion region actuators neither requires etching of narrow gaps, which is technically challenging nor is there a need for introducing piezoelectric materials into the fabrication process flow. The simple operating principle and the possibility of exploiting the technique for various optimized linear or nonlinear actuation at small scales provide opportunities for precise electro-mechanical transduction for micro- and nano-mechanical devices. These actuators are therefore suited for the co-fabrication of micro- and nano-mechanical systems and microelectronic circuits. Additionally, the produced strains depend only on the depletion region specifications and the excitation voltage and do not scale with device dimensions. As such, depletion region actuators can be candidates for efficient nanoscale electromechanical actuation.
Highlights
We are reporting on the fabrication and characterization of microscale electromechanical actuators driven by the internal forces induced within the depletion region of a typical pn junction
Two approaches are presently pursued by the developers of such systems: (a) Chip-level integration within a sub-optimal manufacturing technology based on compromises between micromechanical and microelectronic fabrication technologies; and (b) System-in-package integration, with separate dies for the Micro-Electromechanical Systems (MEMS) and Integrated Circuit (IC) components with compromises on size, performance, and cost
The operation of depletion region actuators (DRA) is based on the net space charge that exists within the depletion region of a pn junction
Summary
We are reporting on the fabrication and characterization of microscale electromechanical actuators driven by the internal forces induced within the depletion region of a typical pn junction. While the microelectronic manufacturing industry is essentially based on fabricating Complementary Metal Oxide Semiconductor (CMOS) transistors, the micromechanical devices mainly employ electrostatic actuation (based on Coulomb force between charged objects) and sensing (based on measurement of changes in capacitance)[2]. The most effective method to improve electromechanical coupling efficiency for single devices, has been the reduction of the electrostatic gap to sub-micron levels through structural layers that can be up to tens of microns thick[6,7]. Realizing such narrow gaps is technically challenging, but it compromises the linear dynamic range of these devices. As device dimensions are decreased, the heat losses through device anchors to the substrate will result in further inefficiencies in electro-mechanical transduction for these devices
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