Monolithic silicon opto-electro-mechanical light modulator
Department of Electrical and Computer Engineering
Master of Science
Carr, William N.
Marcus, Robert Boris
Farmer, Kenneth Rudolph
A Fabry-Perot light beam modulator of the reflection-type has been designed with process and performance parameters optimized. This design takes advantage of the economies of surface micromaching using silicon substrates and selected thin films. High performance with a low drive voltage are achieved using electrostatic actuation of a thin polysilicon diaphragm. The diaphragm is a novel corrugated structure which has maximum compliance and maintains planarity during actuation. In addition, the corrugationsuspension used provides an improved linearity of amplitude modulation response as a function of the actuation voltage.
A preliminary version of this device has been fabricated through a contract foundry using some industry- standard film thicknesses. The preliminary version of the device confirms the physical mask design without optimal film processing. The optimized Fabry-Perot structure is designed for operation at a wavelength of 1.3 nm. Using a thin, corrugated diaphragm of 190 nm thickness a 48.90% modulation index is obtained with an actuation voltage of 5 volts based on detailed simulation results. The final optimized device will be fabricated at NJIT at a future date.
The proposed optimized device contains a titanium-tungsten metal film deposited into a cavity of half wavelength depth and insulated from the monolithic silicon substrate. An additional quarter wavelength film of silicon nitride is deposited over the metal to increase the modulation index. In the fabrication process a 325 nm sacrificial film of spinon glass is deposited to fill the cavity and form the spacer between the Fabry-Perot etalon entrance and reflecting surfaces. The optical entrance surface is obtained next in the fabrication process by depositing an infrared-transmissive film of polysilicon. The selected polysilicon thickness is 190 nm or any odd integer multiple of a half wavelength.
This device can be used as an economical light modulator in near-infrared communications and control systems. This device suitable for relatively low bandwidth applications is expected to provide cost and reliability advantages over competing torsion mirror and macro-sized modulators.
njit-etd1993-001 (148 pages ~ 6,871 KB pdf)
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Created July 17, 2003