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This paper reports a simple electrothermomechanical lumped element model (ETM-LEM) that describes the behavior of an electrothermal bimorph actuator. The ETM-LEM is developed by integrating an electrothermal LEM of a heater with a thermomechanical LEM of a bimorph actuator. This new LEM uses only one power source in both the electrical and thermal domains. The LEM provides a simple and accurate way of relating the output mechanical response of a bimorph actuator to the electrical inputs. The model shows that the tip angular rotation of the bimorph actuator is linearly proportional to its average temperature change. The LEM predicts a linear relationship between both the average temperature change and bimorph tip angular rotation versus voltage when operated above a certain voltage. The LEM is used to predict the rotation angle of a fabricated electrothermal bimorph micromirror in response to the electrical inputs and produces results that agree with finite element model simulations and experimental data within 15% for all measured parameters.

An ove lm ulti-degree-of-freedom electrothermal micromirror design that uses thermal inverted-series-connected (ISC) bimorph actuators is presented. The ISC bimorph actuators eliminate problems observed in previous designs that use single bimorph actuators. The micromirror can operate in one-dimensional (1D) piston-mode and two-dimensional (2D) tilt-mode. Analytical models for the piston-mode and tilt-mode actuations are shown and are compared to FEM simulation results. The device was fabricated using the AMI 1.5 µ mC MOS (complimentary metal-oxide semiconductor) process followed by a post-CMOS micromachining process for device release. The displacement versus temperature of the micromirror was measured experimentally over a range of temperatures and compared to analytical and FEM simulation results .E xperimental results showed that the micromirror displaced by 56 µ ma t an applied temperature 150 ◦ C. The integrated polysilicon heaters were open-circuited during the post-CMOS microfabrication. The failure was caused by pinholes in the metal layers that allowed etchants to attack the polysilicon layer during post-CMOS microfabrication.

This paper reports a novel large vertical displacement (LVD) microactuator that can generate large piston motion and bi-directional scanning at low driving voltage. A LVD micromirror device has been fabricated by using a unique deep reactive ion etch (DRIE) post-CMOS micromachining process that simultaneously provides thin-film and single-crystal silicon microstructures. The bimorph actuation structure is composed of aluminum and silicon dioxide with an embedded polysilicon thermal resistor. With a size of only 0.7 mm × 0.32 mm, the LVD micromirror demonstrated a vertical displacement of 0.2 mm at 6 V dc. This device can also be used to perform bi-directional rotational scanning through the use of two bimorph actuators. The micromirror rotates over ±15 ◦ at less than 6 V dc, and over ±43 ◦ (i.e., >170 ◦ optical scan angle) at its resonant frequency of 2.6 kHz.

A new electrothermal micromirror with large piston and tilt motions was proposed and fabricated. Large initial tilt angles and optical path shifting of previously fabricated thermal micro mirrors were eliminated by employing inverted-series-connected (ISC) bimorph actuators

We have developed an analytical model that describes the steady-state thermal behavior of a 1-D electrothermal bimorph MEMS micromirror. The steady-state 1-D heat transport equation is used to solve for the temperature distribution of the device upon actuation. Three models are developed using different thermal conditions on the device. The models consider heat dissipation from conduction and convection and the temperature dependence of the actuator electrical resistor. The temperature distribution equation of each model is analyzed to find critical thermal parameters such as the position of maximum temperature, maximum temperature, average temperature, and equivalent thermal resistance. The simplest model, called the Case 1 model, is used to develop an electrothermal lumped element model that uses a single thermal power source. In the Case 1 model, it is shown that a parameter called the “balancing factor” predicts where the maximum temperature is located, the distribution of power flow, and the division of thermal resistances. The analytical models are compared to FEM simulations and agree within 20% for all of the actuation ranges and thermal conditions tested.

This paper reports a novel large-vertical-displacement (LVD) microactuator that can generate large piston motion at low driving voltage. A LVD micromirror device has been fabricated by using a unique DRIE CMOS-MEMS process that can simultaneously provide thin-film and single-crystal silicon microstructures. With only a 0.7 mm by 0.32 mm sized device, the LVD micromirror demonstrated a vertical displacement of 0.2 mm at an actuation voltage of 6 V d.c. This device can also perform bidirectional rotational scanning through the use of two bimorph actuators. The micromirror can rotate ± 20q, and has negligible initial tilt angle and high scanning speeds (~2 kHz).

This paper reports a 1mm-by-1mm single-crystal silicon (SCS)-based aluminum-coated micromirror (Fig. 1) that rotates 36° at a 7.5 mA d.c. current. Large, flat micromirrors with large scanning angles are required by applications such as medical imaging and interferometer systems. SCS micromirrors have been explored because of the manufacturability and flatness of SCS-based microstructures [1,2,3]. A previous SCS micromirror rotated 17° at 15 mA (d.c.) [3]. However, the buckling of the employed bimorph mesh structure resulted in a discontinuity in the angle versus current curve, which limited the usable scanning range to about 5°. From FEM simulation (Coventorware) we found that the orientation of the embedded poly-silicon resistor significantly changes the temperature behavior of the micromirror. Fig. 2 illustrates the difference between a previous design and the new design. The new design (Fig. 2(c)) has a transversely oriented serpentine poly-silicon resistor to obtain uniform heating along the transverse direction. This results in a continuous response curve (Fig. 2), and an even larger rotation angle. The micromirror is fabricated using deep reactive-ion-etch (DRIE) CMOS-MEMS processing [4].