Correction: Integrated silicon photonic MEMS.

[This corrects the article DOI: 10.1038/s41378-023-00498-z.].

Correction: Integrated 4-terminal single-contact nanoelectromechanical relays implemented in a silicon-on-insulator foundry process.

Correction for 'Integrated 4-terminal single-contact nanoelectromechanical relays implemented in a silicon-on-insulator foundry process' by Yingying Li et al., Nanoscale, 2023, https://doi.org/10.1039/d3nr03429a.

Integrated 4-terminal single-contact nanoelectromechanical relays implemented in a silicon-on-insulator foundry process.

Integrated nanoelectromechanical (NEM) relays can be used instead of transistors to implement ultra-low power logic circuits, due to their abrupt turn off characteristics and zero off-state leakage. Further, realizing circuits with 4-terminal (4-T) NEM relays enables significant reduction in circuit device count compared to conventional transistor circuits. For practical 4-T NEM circuits, however, the relays need to be miniaturized and integrated with high-density back-end-of-line (BEOL) interconnects, which is challenging and has not been realized to date. Here, we present electrostatically actuated silicon 4-T NEM relays that are integrated with multi-layer BEOL metal interconnects, implemented using a commercial silicon-on-insulator (SOI) foundry process. We demonstrate 4-T switching and the use of body-biasing to reduce pull-in voltage of a relay with a 300 nm airgap, from 15.8 V to 7.8 V, consistent with predictions of the finite-element model. Our 4-T NEM relay technology enables new possibilities for realizing NEM-based circuits for applications demanding harsh environment computation and zero standby power, in industries such as automotive, Internet-of-Things, and aerospace.

Integrated silicon photonic MEMS.

Silicon photonics has emerged as a mature technology that is expected to play a key role in critical emerging applications, including very high data rate optical communications, distance sensing for autonomous vehicles, photonic-accelerated computing, and quantum information processing. The success of silicon photonics has been enabled by the unique combination of performance, high yield, and high-volume capacity that can only be achieved by standardizing manufacturing technology. Today, standardized silicon photonics technology platforms implemented by foundries provide access to optimized library components, including low-loss optical routing, fast modulation, continuous tuning, high-speed germanium photodiodes, and high-efficiency optical and electrical interfaces. However, silicon's relatively weak electro-optic effects result in modulators with a significant footprint and thermo-optic tuning devices that require high power consumption, which are substantial impediments for very large-scale integration in silicon photonics. Microelectromechanical systems (MEMS) technology can enhance silicon photonics with building blocks that are compact, low-loss, broadband, fast and require very low power consumption. Here, we introduce a silicon photonic MEMS platform consisting of high-performance nano-opto-electromechanical devices fully integrated alongside standard silicon photonics foundry components, with wafer-level sealing for long-term reliability, flip-chip bonding to redistribution interposers, and fibre-array attachment for high port count optical and electrical interfacing. Our experimental demonstration of fundamental silicon photonic MEMS circuit elements, including power couplers, phase shifters and wavelength-division multiplexing devices using standardized technology lifts previous impediments to enable scaling to very large photonic integrated circuits for applications in telecommunications, neuromorphic computing, sensing, programmable photonics, and quantum computing.

Vacuum-sealed silicon photonic MEMS tunable ring resonator with an independent control over coupling and phase.

Ring resonators are a vital element for filters, optical delay lines, or sensors in silicon photonics. However, reconfigurable ring resonators with low-power consumption are not available in foundries today. We demonstrate an add-drop ring resonator with the independent tuning of round-trip phase and coupling using low-power microelectromechanical (MEMS) actuation. At a wavelength of 1540 nm and for a maximum voltage of 40 V, the phase shifters provide a resonance wavelength tuning of 0.15 nm, while the tunable couplers can tune the optical resonance extinction ratio at the through port from 0 to 30 dB. The optical resonance displays a passive quality factor of 29 000, which can be increased to almost 50 000 with actuation. The MEMS rings are individually vacuum-sealed on wafer scale, enabling reliable and long-term protection from the environment. We cycled the mechanical actuators for more than 4 × 109 cycles at 100 kHz, and did not observe degradation in their response curves. On mechanical resonance, we demonstrate a modulation increase of up to 15 dB, with a voltage bias of 4 V and a peak drive amplitude as low as 20 mV.

Micro-transfer printing InP C-band SOAs on advanced silicon photonics platform for lossless MZI switch fabrics and high-speed integrated transmitters.

We present an approach for the heterogeneous integration of InP semiconductor optical amplifiers (SOAs) and lasers on an advanced silicon photonics (SiPh) platform by using micro-transfer-printing (µTP). After the introduction of the µTP concept, the focus of this paper shifts to the demonstration of two C-band III-V/Si photonic integrated circuits (PICs) that are important in data-communication networks: an optical switch and a high-speed optical transmitter. First, a C-band lossless and high-speed Si Mach-Zehnder interferometer (MZI) switch is demonstrated by co-integrating a set of InP SOAs with the Si MZI switch. The micro-transfer-printed SOAs provide 10 dB small-signal gain around 1560 nm with a 3 dB bandwidth of 30 nm. Secondly, an integrated transmitter combining an on-chip widely tunable laser and a doped-Si Mach-Zehnder modulator (MZM) is demonstrated. The laser has a continuous tuning range over 40 nm and the transmitter is capable of 40 Gbps non-return-to-zero (NRZ) back-to-back transmission at wavelengths ranging from 1539 to 1573 nm. These demonstrations pave the way for the realization of complex and fully integrated photonic systems-on-chip with integrated III-V-on-Si components, and this technique is transferable to other material films and devices that can be released from their native substrate.

Micro-transfer-printed narrow-linewidth III-V-on-Si double laser structure with a combined 110 nm tuning range.

In this work, we demonstrate for the first time a narrow-linewidth III-V-on-Si double laser structure with more than a 110 nm wavelength tuning range realized using micro-transfer printing (µTP) technology. Two types of pre-fabricated III-V semiconductor optical amplifiers (SOAs) with a photoluminescence (PL) peak around 1500 nm and 1550 nm are micro-transfer printed on two silicon laser cavities. The laser cavities are fabricated in imec's silicon photonics (SiPh) pilot line on 200 mm silicon-on-insulator (SOI) wafers with a 400 nm thick silicon device layer. By combining the outputs of the two laser cavities on chip, wavelength tunability over S+C+L-bands is achieved.

Silicon photonic microelectromechanical phase shifters for scalable programmable photonics.

Programmable photonic integrated circuits are emerging as an attractive platform for applications such as quantum information processing and artificial neural networks. However, current programmable circuits are limited in scalability by the lack of low-power and low-loss phase shifters in commercial foundries. Here, we demonstrate a compact phase shifter with low-power photonic microelectromechanical system (MEMS) actuation on a silicon photonics foundry platform (IMEC's iSiPP50G). The device attains (2.9π±π) phase shift at 1550 nm, with an insertion loss of (0.33-0.10+0.15)dB, a Vπ of (10.7-1.4+2.2)V, and an Lπ of (17.2-4.3+8.8)µm. We also measured an actuation bandwidth f-3dB of 1.03 MHz in air. We believe that our demonstration of a low-loss and low-power photonic MEMS phase shifter implemented in silicon photonics foundry compatible technology lifts a main roadblock toward the scale-up of programmable photonic integrated circuits.

Compact broadband suspended silicon photonic directional coupler.

Directional couplers are extensively used in photonic integrated circuits as basic components for efficient on-chip photonic signal routing. Conventionally, directional couplers are fully encapsulated in the technology's waveguide cladding material. In this Letter, we demonstrate a compact broadband directional coupler, fully suspended in air and exhibiting efficient power coupling in the cross state. The coupler is designed and built based on IMEC's iSiPP50G standard platform, and hydrofluoric (HF) vapor-etching-based post-processing allows to release the freestanding component. A low insertion loss of 0.5 dB at λ=1560nm and a 1 dB bandwidth of 35 nm at λ=1550nm have been confirmed experimentally. With a small footprint of 20µm×30µm and high mechanical stability, this directional coupler can serve as a basic building block for large-scale silicon photonic microelectromechanical systems (MEMS) circuits.

In vitro evaluation of experimental light activated gels for tooth bleaching.

Dental bleaching is an important part of aesthetic dentistry. Various strategies have been created to enhance the bleaching efficacy. As one such strategy, light-activated nanoparticles that enable localized generation of reactive oxygen species have been developed. Here, we evaluated the cellular response to experimental gels containing these materials in in vitro models. L-929 cells, 3T3 cells, and gingival fibroblasts were exposed to the gels at 50%, 10%, 2%, 0.4%, 0.08%, 0.016%, and 0.0032%. The gels contained TiO2/Ag nanoparticles, TiO2 nanoparticles, hydrogen peroxide (6% hydrogen peroxide), or no added component and were tested with and without exposure to light. Cells were exposed to gels for 24 h or for 30 min. The latter case mimics the clinical situation of a short bleaching gel exposure. Metabolic activity and cell viability were evaluated with MTT and neutral red assays, respectively. We found a dose-dependent reduction of formazan formation and neutral red staining with gels containing TiO2/Ag nanoparticles or TiO2 nanoparticles in the 24 h setting with and without illumination. The strongest reduction, which was not dose-dependent in the evaluated concentrations, was found for the gel containing hydrogen peroxide. Gels with TiO2 nanoparticles showed a similar response to gel without particles. TiO2/Ag gel showed a slightly higher impact. When the gels were removed by rinsing after 30 min of exposure without light illumination, gel containing TiO2/Ag nanoparticles showed a stronger reduction of formazan formation and neutral red staining than gel containing TiO2 particles. Exposure of cells for 30 min under illumination and consequent rinsing off the gels also showed that Ag-containing particles can have a higher impact on the metabolic activity and viability than particles from TiO2. Overall our results show that experimental bleaching gels containing TiO2/Ag or TiO2 nanoparticles are less cytotoxic than hydrogen peroxide-containing gel. When gels are removed, gel containing TiO2/Ag particles exhibit a stronger reduction of metabolic activity and viability than the gel containing TiO2.

1.3 µm InAs/GaAs quantum dot DFB laser integrated on a Si waveguide circuit by means of adhesive die-to-wafer bonding.

In this paper we report a single mode InAs/GaAs quantum dot distributed feedback laser at 1.3 µm wavelength heterogeneously integrated on a Si photonics waveguide circuit. Single mode lasing around 1300 nm with a side-mode suppression ratio higher than 40 dB is demonstrated. High temperature operation with continuous wave lasing up to 100°C is obtained. Threshold current densities as low as 205 A/cm2 were measured. These devices are attractive candidates to use in uncooled silicon photonic transceivers in data centers.

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.

Insight in the chemistry of laser-activated dental bleaching.

The use of optical radiation for the activation of bleaching products has not yet been completely elucidated. Laser light is suggested to enhance the oxidizing effect of hydrogen peroxide. Different methods of enhancing hydrogen peroxide based bleaching are possible. They can be classified into six groups: alkaline pH environment, thermal enhancement and photothermal effect, photooxidation effect and direct photobleaching, photolysis effect and photodissociation, Fenton reaction and photocatalysis, and photodynamic effect.

Laser teeth bleaching: evaluation of eventual side effects on enamel and the pulp and the efficiency in vitro and in vivo.

Light and heat increase the reactivity of hydrogen peroxide. There is no evidence that light activation (power bleaching with high-intensity light) results in a more effective bleaching with a longer lasting effect with high concentrated hydrogen peroxide bleaching gels. Laser light differs from conventional light as it requires a laser-target interaction. The interaction takes place in the first instance in the bleaching gel. The second interaction has to be induced in the tooth, more specifically in the dentine. There is evidence that interaction exists with the bleaching gel: photothermal, photocatalytical, and photochemical interactions are described. The reactivity of the gel is increased by adding photocatalyst of photosensitizers. Direct and effective photobleaching, that is, a direct interaction with the colour molecules in the dentine, however, is only possible with the argon (488 and 415 nm) and KTP laser (532 nm). A number of risks have been described such as heat generation. Nd:YAG and especially high power diode lasers present a risk with intrapulpal temperature elevation up to 22°C. Hypersensitivity is regularly encountered, being it of temporary occurrence except for a number of diode wavelengths and the Nd:YAG. The tooth surface remains intact after laser bleaching. At present, KTP laser is the most efficient dental bleaching wavelength.

An octave-spanning mid-infrared frequency comb generated in a silicon nanophotonic wire waveguide.

Laser frequency combs, sources with a spectrum consisting of hundred thousands evenly spaced narrow lines, have an exhilarating potential for new approaches to molecular spectroscopy and sensing in the mid-infrared region. The generation of such broadband coherent sources is presently under active exploration. Technical challenges have slowed down such developments. Identifying a versatile highly nonlinear medium for significantly broadening a mid-infrared comb spectrum remains challenging. Here we take a different approach to spectral broadening of mid-infrared frequency combs and investigate CMOS-compatible highly nonlinear dispersion-engineered silicon nanophotonic waveguides on a silicon-on-insulator chip. We record octave-spanning (1,500-3,300 nm) spectra with a coupled input pulse energy as low as 16 pJ. We demonstrate phase-coherent comb spectra broadened on a room-temperature-operating CMOS-compatible chip.

Silicon dual-ring modulator driven by differential signal.

A silicon dual-ring modulator consisting of two serially cascaded rings with embedded PN junctions is driven by a differential signal pair. We show by simulation and experiment that the device has advantages over the single-ring modulator in terms of optical bandwidth, 3-dB modulation bandwidth and bit rate, at the expense of a 1.7-dB increase in the transmission penalty and a twofold increase of the RF power consumption. Driven by differential pseudo random binary sequence (PRBS) signals of 0.5-V peak-to-peak voltage (Vpp), the dual-ring modulator exhibits optical bandwidths of 66 pm and 40 pm at 12.5 Gb/s and 20 Gb/s, respectively. In contrast, the single-ring modulator has an optical bandwidth of 26 pm under a single-end PRBS signal of 0.5 Vpp at 12.5 Gb/s, and its eye diagram closes if the bit rate rises to 20 Gb/s.

Impact of ALD grown passivation layers on silicon nitride based integrated optic devices for very-near-infrared wavelengths.

A CMOS compatible post-processing method to reduce optical losses in silicon nitride (Si(3)N(4)) integrated optical waveguides is demonstrated. Using thin layer atomic layer deposition (ALD) of aluminum oxide (Al(2)O(3)) we demonstrate that surface roughness can be reduced. A 40 nm thick Al(2)O(3) layer is deposited by ALD over Si(3)N(4) based strip waveguides and its influence on the surface roughness and the waveguide loss is studied. As a result, an improvement in the waveguide loss, from very high loss (60 dB/cm) to low-loss regime (~5 dB/cm) is reported for a 220 nm x 500 nm Si(3)N(4) wire at 900 nm wavelength. This opens prospects to implement very low loss waveguides.

Silicon-organic hybrid (SOH) IQ modulator using the linear electro-optic effect for transmitting 16QAM at 112 Gbit/s.

Advanced modulation formats call for suitable IQ modulators. Using the silicon-on-insulator (SOI) platform we exploit the linear electro-optic effect by functionalizing a photonic integrated circuit with an organic χ(2)-nonlinear cladding. We demonstrate that this silicon-organic hybrid (SOH) technology allows the fabrication of IQ modulators for generating 16QAM signals with data rates up to 112 Gbit/s. To the best of our knowledge, this is the highest single-polarization data rate achieved so far with a silicon-integrated modulator. We found an energy consumption of 640 fJ/bit.

Using carrier-depletion silicon modulators for optical power monitoring.

Defect-mediated subbandgap absorption is observed in ion-implanted silicon-on-oxide waveguides that experience a rapid thermal annealing at 1075°C. With this effect, general carrier-depletion silicon modulators exhibit the capability of optical power monitoring. Responsivity is measured to be 22 mA/W for a 3 mm long Mach-Zehnder modulator of 2×10(18) cm(-3) doping concentration at -7.1 V bias voltage and 5.9 mA/W for a ring modulator of 1×10(18) cm(-3) doping concentration at -10 V bias voltage. The former is used to demonstrate data detection of up to 35 Gbits/s.

Performance tradeoff between lateral and interdigitated doping patterns for high speed carrier-depletion based silicon modulators.

Carrier-depletion based silicon modulators with lateral and interdigitated PN junctions are compared systematically on the same fabrication platform. The interdigitated diode is shown to outperform the lateral diode in achieving a low VπLπ of 0.62 V∙cm with comparable propagation loss at the expense of a higher depletion capacitance. The low VπLπ of the interdigitated PN junction is employed to demonstrate 10 Gbit/s modulation with 7.5 dB extinction ration from a 500 µm long device whose static insertion loss is 2.8 dB. In addition, up to 40 Gbit/s modulation is demonstrated for a 3 mm long device comprising a lateral diode and a co-designed traveling wave electrode.