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In this paper, we review the recent optimization work in hybrid silicon microring lasers. Device structure and fabrication procedures are discussed first, followed by two major improvements in carrier injection and thermal management. A simple, well-controlled quantum well undercut leads to about 20% enhancement of injection efficiency. A silicon-on-diamond (SOD) substrate is demonstrated to fundamentally solve the device heating issue for silicon-on-insulator (SOI)-based active devices. SOD rib waveguides show low propagation loss of 0.74 dB/cm, which is 0.2 dB/cm higher than SOI counterparts. More than 22× reduction of device heating in hybrid silicon microring lasers is projected by simulations.

There are places in this paper where the transducer convection thermal resistance is incorrectly noted as RTC. Wherever RTC is mentioned in the paper it should be replaced with RCA, which was originally defined as the transducer convection thermal resistance in the last line of the first column on p 2266. This error occurs in equations (9), (15), (18) and (21). It also occurs in the second line of the first column on p 2267.

A simple, complementary metal-oxide-semiconductor (CMOS)-compatible fabrication technique is developed to demonstrate a robust silicon-on-diamond (SOD) substrate. The 2.5 μm × 700 nm waveguides with a spiral structure are fabricated on both SOD and conventional silicon-on-insulator (SOI) substrates, showing 0.74- and 0.54-dB/cm propagation loss, respectively. Finite element method (FEM) thermal simulation shows over 3× improvement in heat dissipation on a hybrid silicon laser structure when Si substrate is not a limiting factor.

Low-loss optical rib waveguides (2.5 μm × 700 nm) have been fabricated on a silicon-on-diamond (SOD) substrate. 0.74 dB/cm propagation loss is measured. Benefits to heat dissipation for active photonic devices are studied.

A silicon micromachining process has been developed to fabricate high-aspect-ratio coplanar waveguide (hicoplanar). A new closed-form analytical transmission line model that is valid for both conventional coplanar waveguide (CPW) and hicoplanar is introduced and compared with simulations and experimental results. The major novelties of the model are that it includes the effect of the conductor height on the output parameters and combines Wheeler's inductance rule and perturbation theory to predict the line resistance. Transmission lines with characteristic impedances of 18-25 Ω have been fabricated on high-resistivity silicon. Attenuation was measured to be 2.4-3.4 dB/cm at 30 GHz before silicon removal and 1.7-2.4 dB/cm at 30 GHz after silicon removal. The analytical model is compared with Ansoft High Frequency Structure Simulator simulations and experimental data and shows excellent agreement.

A micromachining process has been developed to create high impedance and low loss high aspect ratio coplanar waveguide (HARC) on low resistivity silicon. The process uses silicon DRIE to create an array of tall mesas that are spaced with a precise pitch. The silicon mesa array is then merged into a single solid SiO2 mesa using thermal oxidation. The solid SiO2 mesa creates a wide dielectric for use in high impedance HARC. The complete fabrication process includes DRIE, thermal oxidation, electroplating, planarization, and substrate removal to create HARC on low resistivity silicon with a planar surface. A high impedance HARC has been fabricated on silicon using this method. Measurements show that silicon substrate removal increases the line impedance from ∼ 20 Ohms to 57 Ohms, reduces effective dielectric constant from ∼ 6 to 2, and reduces attenuation constant from ∼ 33 dB/cm to 4 dB/cm @ 30 GHz. Measurements are compared to an analytical model derived for HARC.

A silicon micromachining process has been developed to fabricate high aspect ratio CPW (HARC). The micromachining process combines Si DRIE, thermal oxidation, electroplating, and planarization to create tall CPW with Au conductors and SiO 2 dielectrics. Si is removed underneath the transmission lines to minimize the field interaction with the substrate which virtually eliminates substrate loss. It is shown that HARC has better loss and isolation compared to microstrip and conventional CPW. Transmission lines with characteristic impedances of 18 – 25 Ω have been fabricated on high resistivity Si. Attenuation was measured to be 2.4 – 3.4 dB/cm at 30 GHz before Si removal and 1.7 – 2.4 dB/cm at 30 GHz after Si removal, demonstrating a substantial improvement in loss due to Si removal. Applications of HARC include CMOS MMICs and hybrid microwave circuits.

Micromirrors have extensive applications in optical switches, displays and many other areas. This chapter is dedicated to introducing a new class of single-crystal silicon (SCS) based micromirrors for biomedical imaging applications particularly for optical coherence tomography (OCT). The SCS micromirrors include one-dimensional (1-D) and two-dimensional (2-D) scanning micromirrors and large-vertical-displacement (LVD) phase-only micromirrors. All the 1-D and 2-D micromirrors are 1 mm by 1 mm in size and coated with aluminum for high reflectivity in broad band. All the micromirrors have flat surface due to the thick SCS supporting layer. The measured static rotation angles are more than 30° at less than 15-V drive voltages, and the resonant frequencies are in order of 1 kHz. A large 200-µm static piston motion has been achieved with the LVD micromirror which has a size of only 0.7 mm by 0.32 mm. Design, simulation, modeling, fabrication and experimental results of these thermally-actuated devices are discussed in detail in this chapter. This first section will introduce the operation of OCT and various existing MEMS mirror techniques.

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.

We report a novel single-crystal-silicon (SCS)-based micromirror that can perform large bi-directional scans and can also generate large piston motion. The micromirror rotates over /spl plusmn/15/spl deg/ at less than 6 V dc voltage, and over /spl plusmn/43/spl deg/ (i.e., >170/spl deg/ optical scan angle) at its resonance of 2.4 kHz. A maximum vertical piston motion of 200 /spl mu/m is also achieved with this 700 /spl mu/m-by-320 /spl mu/m device. A circuit model has been developed for electrothermal behavioral simulation and design optimization. The simulation results using the circuit model match the experimental data to within 8%.