Design, simulation and characterization of a MEMS optical scanner

Abstract

This paper reports on the design, simulation and opto-electro-mechanical characterization of a microelectromechanical system (MEMS) scanner actuated by an out-of-plane (vertical) electrothermal actuator that was fabricated using a single layer silicon-on-insulator (SOI) foundry process. The overall size of the scanner, including the micromirror and the actuator, is 2 mm × 1 mm. A maximum static mechanical tilting angle of 5° is achieved at a dc driving voltage of 18 V and current of 23 mA, corresponding to a 10° optical scan angle. The scanner can be operated from dc to low frequencies (the 3 dB bandwidth is from 0 Hz to 80 Hz), which meets the requirement for certain practical opto-electronic systems such as optical coherence tomography (OCT) systems. The scanner has a maximum mechanical tilting angle of 8° at its resonant frequency of 2.19 kHz, corresponding to a total of 16° maximum optical scan angle. Simulations of static and dynamic performances of the scanner have been conducted using finite element method (FEM) software, resulting in outcomes similar to the experimental findings. A thermal response time of 60 ms is calculated numerically using heat flow theory, while a thermal response time of 55.6 ms was experimentally obtained by analysing the intensity distribution of the scanned patterns generated when using a square driving waveform to drive the scanner.

Review of Electrothermal Micromirrors

“…Since the two hot arms expand longer than the center cold beam, the actuator moves vertically at its free end. In 2007, Li et al reported such a micromirror, as shown in Figure 16 a, where an optical scanning angle of 10° was obtained at 18 V dc [ 50 ]. Another similar 2D micromirror reported by the same group is shown in Figure 16 b [ 51 , 52 ], where four actuators were employed to support a gold-coated mirror plate ( Φ 2 mm).…”

“… SEM photos of ( a ) a 1D micromirror (Reprinted from Li et al [ 50 ] with permission of IOP) and ( b ) a 2D micromirror. (Reprinted from Li et al [ 52 ] with permission of IOP).…”

An imaging systen based on a single MEMS scanner and photodetector

“…The detailed process description can be found in the SOIMUMPs design manual [11]. Out-of-plane actuation is used to operate the scanner, and in our design, a "vertical" electrothermal actuator has been implemented [9] to attain out-of-plane scanning. The 3D schematic of the scanner is shown in Figure 4, while the design layout of the scanner is shown in the Figure 5.…”

“…One of the key parts in this configuration is the MEMS scanner. MEMS scanners have been existing for long time, and many types of scanners have been developed using varies driving mechanisms including electrostatic [3], [4], [5], electromagnetic [6], [7], [8], and electrothermal [9], [10]. An electrothermal driven 2-axis scanner has been designed and fabricated using silicon-on-insulator process, and subsequently used in the optical imaging system described here.…”

Manufacture of Micromirror Arrays Using a CMOS-MEMS Technique

“…Micromirrors are among the important optical devices used in scanned display and image systems. They are also applied widely in projection display systems [ 1 ], optical scanners [ 2 ], optical waveguides [ 3 ], and optical switches [ 4 , 5 ], and for signal processing in rear-projection televisions [ 6 ]. Micromirrors allow scanners in point-to-point scanning to produce distortion-corrected images on highly curved surfaces.…”