Jeroen De Coster

Silicon photonics integrated circuits: a manufacturing platform for high density, low power optical I/O’s

Silicon photonics integrated circuits are considered to enable future computing systems with optical input-outputs co-packaged with CMOS chips to circumvent the limitations of electrical interfaces. In this paper we present the recent progress made to enable dense multiplexing by exploiting the integration advantage of silicon photonics integrated circuits. We also discuss the manufacturability of such circuits, a key factor for a wide adoption of this technology.

Fabrication-Tolerant Four-Channel Wavelength-Division-Multiplexing Filter Based on Collectively Tuned Si Microrings

We demonstrate a robust, compact and low-loss four-channel wavelength-division multiplexing (WDM) filter based on cascaded double-ring resonators (2RR) in silicon. The flat-top channel response obtained by the second-order filter design is exploited to compensate for the detrimental effects of local fabrication variations and their associated phase errors on the ring-based filter response. Full wafer-scale characterization of a cascaded, four-channel 2RR filter with channel spacing of 300 GHz shows an average worst-case insertion loss below 1.5 dB and an average worst-case crosstalk below -18 dB across the wafer, representing a substantial improvement over a first-order based ring (1RR) design. The robust 2RR filter design enables the use of a simple collective thermal tuning mechanism to compensate for global fabrication variations as well as for global temperature fluctuations of the WDM filter, the WDM laser source, or both. Highly uniform collective heating is demonstrated using integrated doped silicon heaters. The compact filter footprint of less than 50×50 μm2 per channel enables straightforward scaling of the WDM channel count to 8 channels and beyond. Such low-loss collectively tuned ring-based WDM filters can prove beneficial in scaling the bandwidth density of chip-level silicon optical interconnects.

High-Responsivity Low-Voltage 28-Gb/s Ge p-i-n Photodetector With Silicon Contacts

We report a high-performance germanium waveguide photodetectors (WPDs) without doping in germanium or direct metal contacts on germanium, grown on and contacted through a silicon p-i-n diode structure. Wafer-scale measurements demonstrate high responsivities larger than 1.0 A/W across the C-band and low dark current of ~3 nA at -1 V and ~8 nA at -2 V. Owing to its small dimensions, the Ge WPD exhibits a high optoelectrical 3-dB bandwidth of 20 and 27 GHz at low-bias voltages of -1 and -2 V, respectively, which are sufficient for operation at 28 Gb/s. The reduced processing complexity at the tungsten contact plug module combined with the high responsivity makes these Ge WPD devices particularly attractive for emerging low-cost CMOS-Si photonics transceivers.

Highly Uniform 25 Gb/s Si Photonics Platform for High-Density, Low-Power WDM Optical Interconnects

We report on electro-optical device performance in a fully integrated 25Gb/s Si photonics platform running on a 130-nm CMOS toolset. Extensive uniformity data is presented for ring modulators, Ge photodetectors and compact ring-based WDM filters.

High-Q integrated RF passives and RF-MEMS on silicon

A technology platform is described for the integration of low-loss inductors, capacitors, and MEMS capacitors on a high-resistivity Si substrate. Using this platform the board space area taken up by e.g. a DCS PA output impedance matching circuit can be reduced by 50%. The losses of passive components that are induced by the semi-conducting Si substrate can effectively be suppressed using a combination of surface amorphisation and the use of poly crystalline Si substrates. A MEM switchable capacitor with a capacitance switching factor of 40 and an actuation voltage of 5V is demonstrated. A continuous tuneable dual-gap capacitor is demonstrated with a tuning ratio of 9 using actuation voltages below 15V.

Imec iSiPP25G silicon photonics: a robust CMOS-based photonics technology platform

Silicon photonics has become in the past years an important technology adopted by a growing number of industrial players to develop their next generation optical transceivers. However most of the technology platforms established in CMOS fabrication lines are kept captive or open to only a restricted number of customers. In order to make silicon photonics accessible to a large number of players several initiatives exist around the world to develop open platforms. In this paper we will present imec’s silicon photonics active platform accessible through multi-project wafer runs.

22.5 A 4×20Gb/s WDM ring-based hybrid CMOS silicon photonics transceiver

Silicon photonics (SiPh) has been identified as a prime technology targeting cost-effective short-range optical links [1]. Wavelength-division multiplexing (WDM) is an attractive approach for enabling high aggregate transceiver bandwidth without increasing the number of optical fibers used in the link. Ring-based optical modulators and wavelength-selective filters are attractive devices for scalable WDM SiPh transceivers owing to their compact footprint and moderate power required for thermal tuning. In this paper, we report on a thermally controlled ring-based flip-chip integrated CMOS-SiPh transceiver with 4 channels operating at 20Gb/s.

SiGe MEMS technology: a platform technology enabling different demonstrators

In imecs 200mm fab a dedicated poly-SiGe above-IC MEMS (Micro Electro-Mechanical Systems) platform has been set up to integrate MEMS and its readout and driving electronics on one chip. In the Flemish project Gemini the possibilities of this platform have been further explored together with the project partners. Three different demonstrators were realized: mirrors for display applications, grating light valves (GLV) and accelerometers. Whereas the mirrors and GLVs are made with a similar to 300 nm thick SiGe structural layer plus optical coating, the SiGe structural layer thickness for the accelerometers is 4 mu m in order to improve the capacitive readout of in-plane devices. The processing and measurement results of these functional demonstrators are shown in this paper. These new demonstrators reconfirm the generic nature of the SiGe MEMS platform.

High‐Damping Carbon Nanotube Hinged Micromirrors

New developments in digital mirror devices (DMDs) require suspension hinges with a good damping and high temperature stability. Carbon nanotubes (CNTs) offer these unique properties. Herein it is shown how CNT hinges can be integrated in micromirrors. The image illustrates a micromirror with a CNT suspension, and a typical overdamped stepresponse (Q-factor < 0.5).

Submicron three-terminal SiGe-based electromechanical ohmic relay

This paper demonstrates functional NEM cantilever relays fabricated in a CMOS-compatible low-T (400°C) CVD SiGe process flow. Devices with a length in the micrometer range (<;3μm), a width in the range 0.2-1μm, a thickness and a gap of below 100nm were successfully fabricated and characterized. A high on/off current ratio (of better than 10⁸:1), a subthreshold swing (S) better than 150μV/decade and “essentially zero” off-state leakage current were experimentally observed. A life time of minimum 10³ switching cycles was demonstrated. A maximum current density of around 10μA/μm² without causing stiction due to Joule-heating was found.