High-speed silicon electro-optic modulator for electronic photonic integrated circuits

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 173-184).The development of future electronic-photonic integrated circuits (EPIC) based on silicon technology critically depends on the availability of CMOS-compatible high-speed modulators that enable the interaction of electronic and optical signals. This thesis investigates electrically driven Mach-Zehnder modulators based on high-index contrast silicon waveguide technology and electronic carrier injection. Modulators based on four different structures are investigated: the forward-biased PiN diode with and without lifetime reduction, the reverse-biased PIN/PN diode and a metal-oxide-semiconductor (MOS) structure. These devices are compared with each other in terms of achievable performance. A modulator based on the forward-biased PIN diode with lifetime reduction is designed to reach 34GHz bandwidth and a low figure of merit V -. L = 0.6V - cm using a carrier lifetime reduction and a graded doping profile. A bandwidth of 1-2GHz has been demonstrated so far which is considerably smaller than the design bandwidth due to high series resistance. Modulators based on the forward-biased PIN structure without lifetime reduction have a low figure of merit, very low voltage and extremely low power consumption in the low frequency regime.(cont.) The measurements demonstrate a RF power consumption of 100mW for 25% modulation depth and a figure of merit of V, - L = 0.28V - cm at frequencies up to 10GHz. A pre-compensation technique, using a high pass filter which consists of a parallel resistor and capacitor, extends the modulator bandwidth from 100MHz to 5GHz experimentally. Further it is shown that, modulators based on the reverse-biased structure can in principle reach very high speed, up to 40-80GHz in design but it's difficult to reduce V, - L values close to or even below 1V - cm and the necessary drive voltage is higher than the voltage provided by the CMOS technology. For the measured bandwidth of the fabricated devices so far only 1-2GHz has been demonstrated. This discrepancy is caused by the RC delay due to the experimental setup and high contact resistance. Finally, the performance of the modulator based on the metal-on-semiconductor (MOS) structure is analyzed. Furthermore, an electrically driven Mach-Zehnder waveguide modulator based on a high-index contrast silicon split-ridge waveguide (SRW) technology and electronic carrier injection is proposed.(cont.) The excellent optical and carrier confinement possible in high-index contrast waveguide devices, together with the forward biased operation and the good thermal heat sinking due to the silicon slab close to the waveguide, enables high speed modulation with small signal modulation bandwidths beyond 20GHz, a V, times length figure of merit of V, - L = 0.5Vcm and an insertion loss of about 5.3 dB. Finally, all-optical switches based on optical carrier-injection in high index contrast Si/Si02 split-ridge-waveguide (SRW) couplers are proposed. The waveguide devices are suitable for the construction of low-loss optical switch matrices as well as fast optical switching. These devices exhibit robustness against fabrication tolerances, improved heat sinking, good carrier confinement and high uniformity in transmission over the entire C-band of optical communications in contrast to comparable devices based on buried or ridge waveguides. A reasonably low electrical switching power of 1-10mW is predicted for switching frequencies in the 1MHz-1GHz range. Faster switching speed can be achieved by carrier lifetime reduction.by Fuwan Gan.Ph.D

Performance Comparison of Phase Change Materials and Metal-Insulator Transition Materials for Direct Current and Radio Frequency Switching Applications

Advanced understanding of the physics makes phase change materials (PCM) and metal-insulator transition (MIT) materials great candidates for direct current (DC) and radio frequency (RF) switching applications. In the literature, germanium telluride (GeTe), a PCM, and vanadium dioxide (VO2), an MIT material have been widely investigated for DC and RF switching applications due to their remarkable contrast in their OFF/ON state resistivity values. In this review, innovations in design, fabrication, and characterization associated with these PCM and MIT material-based RF switches, have been highlighted and critically reviewed from the early stage to the most recent works. We initially report on the growth of PCM and MIT materials and then discuss their DC characteristics. Afterwards, novel design approaches and notable fabrication processes; utilized to improve switching performance; are discussed and reviewed. Finally, a brief vis-á-vis comparison of resistivity, insertion loss, isolation loss, power consumption, RF power handling capability, switching speed, and reliability is provided to compare their performance to radio frequency microelectromechanical systems (RF MEMS) switches; which helps to demonstrate the current state-of-the-art, as well as insight into their potential in future applications

A compound figure of merit for photonic applications of metal nanocomposites

Selecting nanocomposites for photonic switching applications requires optimizing their thermal, nonlinear and two-photon absorption characteristics. We simplify this step by defining a compound figure of merit (FOM_{C}) for nanocomposites of noble metals in dielectric based on criteria that limit these structures in photonic applications, i.e. thermal heating and two-photon absorption. The device independent results predict extremely large values of FOM_{C} for a specific combination of the metal and insulator dielectric constant given by \epsilon_{h}=\frac{\epsilon_{1}-\epsilon_{2}}{2}, where \epsilon_{h} is the dielectric constant of the host and \epsilon_{1} and \epsilon_{2} are the real and imaginary parts for the metal.Comment: Appearing in Appl. Phys. Lett. (2006

Diamond semiconductor technology for RF device applications

This paper presents a comprehensive review of diamond electronics from the RF perspective. Our aim was to find and present the potential, limitations and current status of diamond semiconductor devices as well as to investigate its suitability for RF device applications. While doing this, we briefly analysed the physics and chemistry of CVD diamond process for a better understanding of the reasons for the technological challenges of diamond material. This leads to Figure of Merit definitions which forms the basis for a technology choice in an RF device/system (such as transceiver or receiver) structure. Based on our literature survey, we concluded that, despite the technological challenges and few mentioned examples, diamond can seriously be considered as a base material for RF electronics, especially RF power circuits, where the important parameters are high speed, high power density, efficient thermal management and low signal loss in high power/frequencies. Simulation and experimental results are highly regarded for the surface acoustic wave (SAW) and field emission (FE) devices which already occupies space in the RF market and are likely to replace their conventional counterparts. Field effect transistors (FETs) are the most promising active devices and extremely high power densities are extracted (up to 30 W/mm). By the surface channel FET approach 81 GHz operation is developed. Bipolar devices are also promising if the deep doping problem can be solved for operation at room temperature. Pressure, thermal, chemical and acceleration sensors have already been demonstrated using micromachining/MEMS approach, but need more experimental results to better exploit thermal, physical/chemical and electronic properties of diamond