Metallic Microheaters Research Articles

Fully tunable microwave photonic narrow bandpass filter using an on-chip dual-drive microring resonator.

We propose and experimentally demonstrate a fully tunable microwave photonic narrow bandpass filter based on phase modulation to intensity modulation (PM-IM) conversion. In the filter implementation, an on-chip dual-drive microring resonator (MRR) is a key component. This resonator leverages a multimode waveguide to enable a high Q-factor. A metallic micro-heater and a lateral PN junction are simultaneously created for resonance wavelength tuning. When one driving signal is applied to the micro-heater, a large tuning range of the resonance wavelength is resulted; when another driving signal is applied to the PN junction, a fast tuning speed of the resonance wavelength is caused. By jointly using two different tuning mechanisms, the realized microwave photonic filter features a large frequency tuning range as well as a fast tuning speed. In addition, the filter bandwidth can also be tuned. A silicon-based dual-drive high-Q racetrack MRR chip is designed, fabricated, and evaluated. By incorporating the chip in a microwave photonic filter system, a bandpass filter with a narrow bandwidth of 1.27 GHz is achieved. An ultra-wide frequency tuning range from 3 to 51 GHz, an ultra-fast tuning speed less than 0.54 ns, and a tunable bandwidth from 1.27 to 4.47 GHz is experimentally demonstrated. This fully tunable filter offers significant potential in future radar and next-generation wireless communication applications.

Fully Reconfigurable Fano Resonator on a Silicon Photonic Chip

A fully reconfigurable Fano resonator on a silicon photonic chip is reported. The Fano resonator is realized with the use of an add-drop micro-disk resonator (MDR) and a Mach-Zehnder interferometer (MZI). The waveguides at the through and drop ports of the MDR connect to two spiral waveguide arms of the MZI directly. Two independent metallic micro-heaters are incorporated on top of the MDR and the lower arm of the MZI. Thanks to the resonant mode interference between the MDR and the MZI, the Fano resonance occurs. By thermal tuning the resonance coupling between the MDR and the MZI, the generated Fano resonance is fully tunable. In addition to the independent tunable slope rate (SR) and the resonance wavelength, the Fano resonance wavelength can shift while its line shape remains by simultaneously controlling the two micro-heaters. A chip is designed, fabricated and evaluated. The measurement results show that the static Fano resonance has a line shape with an extinction ratio (ER) of 17.1 dB and SR of −13.6 dB/nm. By simultaneously controlling the two micro-heaters, full reconfigurability of the Fano resonance is demonstrated. Thanks to its straightforward configuration, the proposed Fano resonator holds the key advantage in terms of ultra-compactness and fully reconfigurability, which offers a great potential for applications such as on-chip optical switching, modulation and microwave photonics applications.

Laser multifunctional fabrication of metallic microthermal components embedded in fused silica for microfluidic applications

Microheaters as tiny in-situ heating elements are of great importance for developing many thermal-sensitive microdevice applications. A facile technique for the fabrication of embedded metallic microheaters, microheater arrays, and microthermal sensors based on the combination of femtosecond laser-assisted chemical etching, electroless plating, and mechanical polishing has been proposed. With the proposed technique, uniform and controllable temperature distributions in the central area of fabricated microheaters have been achieved. Moreover, flexible manipulation of localized temperature in a microheater array as well as precise calibration of microheaters based on a simultaneously integrated microthermal sensor has been demonstrated. Furthermore, precise control of temperature in glass channels and acceleration of a chemical reaction in microfluidics using monolithically integrated microheaters have been realized, showing great potential for developing laser manufacturing of multifunctional thermal-control microfluidic devices.

1 × 2 Switchable Dual-Mode Optical 90° Hybrid Device Based on Thermo-Optic Phase Shifters and 2 × 2 MMI Couplers on SOI Platform

This paper designs a 1 × 2 switchable dual-mode optical 90° hybrid device on the silicon-on-insulator (SOI) platform for the mode division multiplexing hybridized coherent transmission systems in optical communication. Our proposed hybrid uses various 2 × 2 multimode interference (MMI) couplers, symmetric Y-junctions, and thermo-optic phase shifters. The suggested hybrid device working principle is proved on theoretical analysis about the multimode interference and the transfer matrix relation. The optimization of geometrical parameters and metallic micro-heaters is executed through the numerical simulation method. The proposed hybrid coupler expresses lots of optical performance advantages, with an insertion loss lower than 2.5 dB, a common-mode rejection ratio (CMRR) better than −24 dB, and phase error smaller than 4° in the 50-nm wavelength bandwidth of the third telecom window for both two TE modes. Besides, the device is proven large geometrical tolerances in terms of width and height tolerances larger than ±50 nm and ±6 nm in the 1.5-dB variation limit of transmission, respectively. In addition, the proposed device attains relatively low power consumption under 75 mW and an ultrafast switching time below 10 μs. Such advantages of good performances make the device a promising potential for broadband and intra-chip MDM-hybridized coherent optical communication systems and photonic integrated circuits.

Silicon Photonic Integrated Optoelectronic Oscillator for Frequency-Tunable Microwave Generation

Photonic generation of a frequency-tunable microwave signal based on a silicon photonic integrated optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. The silicon photonic chip includes a high-speed phase modulator (PM), a thermally tunable micro-disk resonator (MDR), and a high-speed photodetector (PD). When an external light wave is injected into the chip, by a joint use of the PM, the MDR, and the PD, a bandpass microwave photonic filter (MPF) based on phase modulation and phase-modulation to intensity-modulation (PM-IM) conversion is realized. If the output microwave signal from the MPF is fed to the microwave input port of the PM with a sufficiently large gain provided by an electrical amplifier, the MPF becomes an OEO. By controlling the electrical power applied to a micro-heater, the resonance frequency of the MDR is tuned, which leads to the tuning of the MPF, and thus, the OEO oscillation frequency. In the experimental demonstration, two silicon photonic integrated OEOs using two MDRs with different micro-heaters are studied. The first OEO has a high-resistivity metallic micro-heater placed on top of the MDR, and the second OEO has a p-type doped silicon heater in the MDR. The two thermally tunable MDRs are characterized, and the performance of the MPFs based on the two MDRs is evaluated. The use of the two MPFs to implement two OEOs is performed, and their performance is evaluated in terms of frequency tunable range, phase noise, and power consumption.

Nonlinear numerical analysis and experimental testing for an electrothermal SU-8 microgripper with reduced out-of-plane displacement

This paper reports the results of numerical nonlinear electro-thermo-mechanical analysis and experimental testing of a polymeric microgripper designed using electrothermal actuators. The simulation work was carried out using a finite element method (FEM) and a commercial software (Coventorware 2014). The biocompatible SU-8 polymer was used as structural material for the fabrication of the microgripper. The metallic micro-heater was encapsulated in the polymeric actuation structures of the microgripper to reduce the undesirable out-of-plane displacement of the microgripper tips, and to electrically isolate the micro-heater, and to reduce the mechanical stress as well as to improve the thermal efficiency. The electro- thermo-mechanical analysis of the actuator considers the nonlinear temperature-dependent properties of the SU-8 polymer and the gold thin film layers used for the micro-heater fabrication. An optical characterisation of the microgripper based on an image tracking approach shows the thermal response and the good repeatability. The average deflection is ~11 µm for an actuation current of ~17 mA. The experimentally obtained tip deflection and the heater temperature at different currents are both shown to be in good agreement with the nonlinear electro-thermo-mechanical simulation results. Finally, we demonstrate the capability of the microgripper by capture and manipulation of cotton fibres.

Miniaturized 3-D Solenoid-Type Micro-Heaters in Coordination With 3-D Microfluidics

We fabricate and characterize a prototype on-chip 3-D micro-heater inside a fused silica chip, which is coordinated with a microfluidic channel. By means of enhanced femtosecond laser wet etching followed by a micro-mold injection process of a liquid metal, the solenoid-type metallic micro-heater, with a size of π × 100 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> × 1120 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , was fabricated twining outward a linear microfluidic channel. The micro-heater exhibits excellent performances, such as precisely current-temperature controllability (temperature range from 0°C to 130°C), rapid heating/cooling process (up to 16 °C/s at the beginning of the heating process and 15.8 °C/s at the beginning of cooling process), and uniform temperature distribution. This work not only provides a high-quality micro-heater for biological or chemical applications, which requires rigid temperature control capabilities, but also proposes a practical route to the fabrication of comprehensive truly-3-D lab-on-a-chip devices and microelectromechanical systems.

Design, numerical simulation and experimental investigation of an SU-8 microgripper based on the cascaded V-shaped electrothermal actuators

This paper presents the numerical simulation results and the experimental investigations of a polymeric microgripper designed using the cascaded V-shaped electrothermal actuators. The microgripper was simulated using electro-thermo-mechanical finite element method (FEM) based on Coventorware 2014 software in order to check the performance of the gripper. As structural material of the microgripper, the SU-8 biocompatible polymer was used during the fabrication process. The metallic micro-heaters were encapsulated in the polymeric actuation structures of the microgrippers to reduce the undesirable out-of-plane displacement of the gripper tips, to reduce the mechanical stress and to improve the thermal efficiency. Experimental testing has been performed to determine the openings of the microgripper tips as function of electrical current. A displacement of the tips of more than 50 pm can be obtained at an electrical current of around 25-26 mA. Over 27-28 mA the heaters are still working but a softening and a damaging status in the polymer were observed.

Modeling and experimental investigation of an integrated optical microheater in silicon-on-insulator.

A linear piecewise model has been formulated to analyze the performance of a metallic microheater integrated with single-mode waveguides (λ∼1550 nm) in silicon-on-insulator (SOI). The model has been used to evaluate integrated optical microheaters fabricated in a SOI substrate with 2 µm device layer thickness. The Fabry-Perot modulation technique has been used to extract the effective thermo-optic phase shift and response time. The effective thermal power budget of Peff,π∼500 µW (out of actually consumed power Pπ=1.1 mW) for a π phase shift and a switching time of τ∼9 µs, have been recorded for a typical Ti heater stripe of length LH=50 µm, width WH=2 µm, and thickness tH∼150 nm, integrated with a Fabry-Perot waveguide cavity of length ∼20 mm. It has been shown that the performance of a heater improves (in terms of power budget) as the length of a microheater decreases. However, smaller heater size requires higher joule heating to obtain a desired phase shift, which is again found to be dependent on polarization of the guided mode because of thermal stress.

Tuning of resonance spacing over whole free spectral range based on Autler-Townes splitting in a single microring resonator

In this paper, a single microring resonator structure formed by incorporating a reflectivity-tunable loop mirror is demonstrated for the tuning of resonance spacing. Autler-Townes splitting in the resonator is utilized to tune the spacing between two adjacent resonances by controlling the strength of coupling between the two counter-propagating degenerate modes in the microring resonator. A theoretical model based on the transfer matrix method is built to analyze the device. The theoretical analysis indicates that the resonance spacing can be tuned from zero to one free spectral range (FSR). In experiment, by integrating metallic microheater, the tuning of resonance spacing in the range of the whole FSR (1.17 nm) is achieved within 9.82 mW heating power dissipation. The device has potential for applications in reconfigurable optical filtering and microwave photonics.

Self-powered transparent flexible graphene microheaters

Transparent and flexible (TF) microheaters are required in wearable devices, labs-on-chip, and micro-reactors. Nevertheless, conventional microheaters are rigid or opaque or both. Moreover, the resistances of conventional metallic microheaters are too low to be effectively powered by wearable energy harvesters. Here, we demonstrate the first TF microheaters by taking advantage of chemical vapor deposition (CVD)-grown graphene heating tracks and of a hexagonal boron nitride (h-BN) sheet for passivation; the h-BN sheet increases the maximum temperature by ~80%. Our TF microheaters show excellent temperature uniformity and can reach temperatures above 200°C in just 4s, with power consumption as low as 39mW. Additionally, since the CVD-graphene sheet resistance is orders of magnitude higher than that of typical metallic heaters, our devices can be effectively powered by wearable energy harvesters. As a proof-of-concept, we demonstrate the first self-powered, wearable microheater which achieves a temperature increase of 8°C when operated by a sound driven textile-based triboelectric nanogenerator. This is a key milestone towards next generation microheaters with applications in portable/wearable personal electronics, wireless health, and remote and mobile environmental sensors.

Optimization of metallic microheaters for high-speed reconfigurable silicon photonics

The strong thermooptic effect in silicon enables low-power and low-loss reconfiguration of large-scale silicon photonics. Thermal reconfiguration through the integration of metallic microheaters has been one of the more widely used reconfiguration techniques in silicon photonics. In this paper, structural and material optimizations are carried out through heat transport modeling to improve the reconfiguration speed of such devices, and the results are experimentally verified. Around 4 micros reconfiguration time are shown for the optimized structures. Moreover, sub-microsecond reconfiguration time is experimentally demonstrated through the pulsed excitation of the microheaters. The limitation of this pulsed excitation scheme is also discussed through an accurate system-level model developed for the microheater response.

Tuning of resonance-spacing in a traveling-wave resonator device

In this work a traveling-wave resonator device is proposed and experimentally demonstrated in silicon-on-insulator platform in which the spacing between its adjacent resonance modes can be tuned. This is achieved through the tuning of mutual coupling of two strongly coupled resonators. By incorporating metallic microheaters, tuning of the resonance-spacing in a range of 20% of the free-spectral-range (0.4nm) is experimentally demonstrated with 27mW power dissipation in the microheater. To the best of our knowledge this is the first demonstration of the tuning of resonance-spacing in an integrated traveling-wave-resonator. It is also numerically shown that these modes exhibit high field-enhancements which makes this device extremely useful for nonlinear optics and sensing applications.

Planar digital nanoliter dispensing system based on thermocapillary actuation

We provide guidelines for the design and operation of a planar digital nanodispensing system based on thermocapillary actuation. Thin metallic microheaters embedded within a chemically patterned glass substrate are electronically activated to generate and control 2D surface temperature distributions which either arrest or trigger liquid flow and droplet formation on demand. This flow control is a consequence of the variation of a liquid's surface tension with temperature, which is used to draw liquid toward cooler regions of the supporting substrate. A liquid sample consisting of several microliters is placed on a flat rectangular supply cell defined by chemical patterning. Thermocapillary switches are then activated to extract a slender fluid filament from the cell and to divide the filament into an array of droplets whose position and volume are digitally controlled. Experimental results for the power required to extract a filament and to divide it into two or more droplets as a function of geometric and operating parameters are in excellent agreement with hydrodynamic simulations. The capability to dispense ultralow volumes onto a 2D substrate extends the functionality of microfluidic devices based on thermocapillary actuation previously shown effective in routing and mixing nanoliter liquid samples on glass or silicon substrates.

Fabrication and thermal evaluation of silicon on diamond wafers

Silicon on diamond (SOD) is proposed as a superior alternative to conventional silicon on insulator (SOI) technology for silicon-based electronics. In this paper, we present a novel SOD structure in which the active Si layer is in direct contact with a thick, highly oriented diamond (HOD) layer that is directly attached to a heat sink. In contrast to the earlier work,1,2 the diamond film is relatively thick (∼70 µm), free standing, and close to single crystalline, thus possessing much greater thermal conductivity and no limitation of the Si backing wafer. Two different fabrication schemes are investigated: (1) direct growth, where the Si-device layer makes contact with the nucleation side of the diamond layer; and (2) wafer fusion, where the Si device layer makes a direct contact with the diamond growth surface. Thermal evaluation was performed using metallic microheaters. These studies clearly showed more than one order of magnitude better thermal management properties of diamond with respect to Si and SOI.

Fabrication and operation of polyimide bimorph actuators for a ciliary motion system

In order to extract macroscopic mechanical work out of microelectromechanical systems, we have proposed the concept of distributed micromotion systems (DMMS). The key idea of DMMS is to coordinate simple motions of many microactuators in order to perform a task. Design, fabrication, and operation of a type of DMMS, called a ciliary motion system, are presented. A bimorph thermal actuator using two types of polyimides with different thermal expansion coefficients and a metallic microheater in between them was fabricated. The cantilever-shaped actuator curled up from the substrate owing to the residual stress in polyimides which built up during the cooling process after they were cured at 350 degrees C. It flattened and moved downward by flowing current in the heater. The dimensions of the cantilever were 500 mu m in length, 100 mu m in width, and 6 mu m in thickness. The tip of the cantilever moved 150 mu m in the direction vertical to the substrate and 80 mu m in the horizontal direction; these were the maximum displacements obtained with 33 mW dissipated in the heater. The cut-off frequency was 10 Hz. On a 1-cm-square substrate, 512 cantilevers were fabricated to form an array. Two sets of cantilevers were placed opposing to each other. We operated them in coordination to mimic the motion and function of cilia and carried a small piece of a silicon wafer (2.4 mg) at 27-500 mu m/s with 4-mW input power to each actuator. >