On-chip Actuation Research Articles

Integration of piezoelectric and electrothermal actuators for high-resolution Atomic Force Microscopy

The development of ultrasensitive silicon-based microcantilevers has significantly improved the imaging resolution of the Atomic Force Microscope (AFM). However, most of these microcantilevers require one or more external actuators and sensors for imaging, thus increasing the footprint and operational complexity of the instrument. Here we propose a novel active microcantilever that does not require any external actuator apart from the sample positioner to perform high-resolution AFM imaging. The proposed microcantilever is equipped with two different on-chip actuators: a piezoelectric actuator for oscillating the probe at a high frequency and an electrothermal actuator for providing large-range Z-motion. An on-chip differential piezoelectric sensor measures probe oscillation during imaging. To demonstrate the proof of concept, the microcantilever was microfabricated and integrated with an in-house developed AFM setup comprising of sample positioner and drive electronics. Finally, 3 different calibration gratings were imaged with a closed-loop bandwidth of 150Hz.

A Multi-Functional CMOS Biosensor Array With On-Chip DEP-Assisted Sensing for Rapid Low-Concentration Analyte Detection and Close-Loop Particle Manipulation With No External Electrodes.

This article presents a fully-integrated dielectrophoresis (DEP)-assisted multi-functional CMOS biosensor array chip with 4096 working electrodes (WEs), 12288 photodiodes (PDs), reference electrodes (REs), and counter electrodes (CEs), while each WE and photodiode can be reconfigured to support on-chip DEP actuation, electrochemical potentiostat, optical shadow imaging, and complex impedance sensing. The proposed CMOS biosensor is an example of an actuation-assisted label-free biosensor for the rapid sensing of low-concentration analytes. The DEP actuator of the proposed CMOS biosensor does not require any external electrode. Instead, on-chip WE pairs can be re-used for DEP actuation to simplify the sensor array design. The CMOS biosensor is implemented in a standard 130-nm BiCMOS process. Theoretical analyses and finite element method (FEM) simulations of the on-chip DEP operations are conducted as proof of concept. Biological assay measurements (DEP actuation/electrochemical potentiostat/impedance sensing) with E.coli bacteria and microbeads (optical shadow imaging) demonstrate rapid detection of low-concentration analytes and simultaneous manipulation and detection of large particles. The on-chip DEP operations draw the analytes closer to the sensor electrode surface, which overcomes the diffusion limit and accelerates low-concentration analyte sensing. Moreover, the DEP-based movement of large particles can be readily detected by on-chip photodiode arrays to achieve close-loop manipulation and sensing of particles and droplets. These show the unique advantages of the DEP-assisted multi-functional biosensor.

Spin-Coated Heterogenous Stacked Electrodes for Performance Enhancement in CMOS-Compatible On-Chip Microsupercapacitors.

Integration of microsupercapacitors (MSCs) with on-chip sensors and actuators with nanoenergy harvesters can improve the lifetime of wireless sensor nodes in an Internet-of-Things (IoT) architecture. However, to be easy to integrate with such harvester technology, MSCs should be fabricated through a complementary-metal-oxide-semiconductor (CMOS) compatible technology, ubiquitous in electrode choice with the capability of heterogeneous stacking of electrodes for modulation in properties driven by application requirements. In this article, we address both these issues through fabrication of multielectrode modular, high energy density microsupercapacitors (MSC) containing reduced graphene oxide (GO), GO-heptadecane-9-amine (GO-HD9A), rGO-octadecylamine (rGO-ODA), and rGO-heptadecane-9-amine (rGO-HD9A) that stack through a scalable, CMOS compatible, high-wafer-yield spin-coating process. Furthermore, we compare the performance of the stack with individual electrode MSCs fabricated through the same process. The individual electrodes, in the presence of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfony)imide (EMIM-TFSI), demonstrate a capacitance of 38, 30, 36, and 105 μF cm–2 at 20 mV s–1 whereas the fabricated stack of electrodes demonstrates a high capacitance of 280 μF cm–2 at 20 mV s–1 while retaining and enhancing the material-dependent capacitance, charge retention, and power density.

Simultaneous tip force and displacement sensing for AFM cantilevers with on-chip actuation: Design and characterization for off-resonance tapping mode

The use of integrated on-chip actuation simplifies the identification of a cantilever resonance, can improve imaging speed, and enables the use of smaller cantilevers, which is required for low-force imaging at high speed. This article describes a cantilever with on-chip actuation and novel dual-sensing capabilities for AFM. The dual-sensing configuration allows for tip displacement and tip force to be measured simultaneously. A mathematical model is developed and validated with finite element analysis. A physical prototype is presented, and its calibration and validation are presented. The cantilever is optimized for use in off-resonance tapping modes. Experimental results demonstrate an agreement between the on-chip sensors and external force and displacement measurements.

Real-time irradiation system using patterned light to actuate light-driven on-chip gel actuators

A light-driven gel actuator is a potential candidate for a single-cell manipulation tool because it allows cells to be manipulated while ensuring less damage. Moreover, a large number of actuators can be integrated into a microfluidic chip because no wiring is required. Previously, we proposed a method for cell manipulation using light-driven gel actuators. However, the system used in the previous work did not allow the targeted cells to be manipulated in real time because the system used in the previous work could only irradiate preprogrammed patterned light. Moreover, when a large number of gel actuators are integrated into a chip, the Gaussian distribution of the laser light source results in the response characteristics of the gel actuators varying with the location of the actuator. In this work, we constructed a system that homogenized the intensity of the patterned light used for irradiation, allowing multiple gel actuators to be driven in parallel in real time. The intensity-homogenized patterned light improved the variations in the response characteristics of the gel actuators, and as a result, we succeeded in actuating gel actuators with various light patterns in real time.

Active atomic force microscope cantilevers with integrated device layer piezoresistive sensors

Active atomic force microscope cantilevers with on-chip actuation and sensing provide several advantages over passive cantilevers which rely on piezoacoustic base-excitation and optical beam deflection measurement. Active microcantilevers exhibit a clean frequency response, provide a path-way to miniturization and parallelization and avoid the need for optical alignment. However, active microcantilevers are presently limited by the feedthrough between actuators and sensors, and by the cost associated with custom microfabrication. In this work, we propose a hybrid cantilever design with integrated piezoelectric actuators and a piezoresistive sensor fabricated from the silicon device layer without requiring an additional doping step. As a result, the design can be fabricated using a commercial five-mask microelectromechanical systems fabrication process. The theoretical piezoresistor sensitivity is compared with finite element simulations and experimental results obtained from a prototype device. The proposed approach is demonstrated to be a promising alternative to conventional microcantilever actuation and deflection sensing.

Evaluation of Three-dimensional Shape and Drive Characteristics of On-chip Gel Actuator

Evaluation of Three-dimensional Shape and Drive Characteristics of On-chip Gel Actuator

Evaluation of the Response Characteristics of On-Chip Gel Actuators for Various Single Cell Manipulations

On-chip gel actuators are potential candidates for single cell manipulation because they can realize low-invasive manipulation of various cells. We propose an on-chip gel actuator driven by light irradiation. By patterning the gel actuator with light absorber, we can control the temperature of the actuator and drive it. The proposed drive method can realize highly localized temperature control of the gel actuator and can be applied to mass integration of on-chip gel actuators. In this study, we evaluate the heat conduction of the actuator during driving and its response characteristics as a function of various design parameters. We theoretically and experimentally evaluate the response characteristics and confirm that the response characteristics can be changed by altering the size of the light absorber. Furthermore, we show some examples of cell manipulation including trapping, transport, and sorting with various sizes of light absorber. Finally, we show proof of concept for the application of the proposed drive method for massive integration of on-chip gel actuators.

Radio-frequency optomechanical characterization of a silicon nitride drum

On-chip actuation and readout of mechanical motion is key to characterize mechanical resonators and exploit them for new applications. We capacitively couple a silicon nitride membrane to an off resonant radio-frequency cavity formed by a lumped element circuit. Despite a low cavity quality factor (QE ≈ 7.4) and off resonant, room temperature operation, we are able to parametrize several mechanical modes and estimate their optomechanical coupling strengths. This enables real-time measurements of the membrane’s driven motion and fast characterization without requiring a superconducting cavity, thereby eliminating the need for cryogenic cooling. Finally, we observe optomechanically induced transparency and absorption, crucial for a number of applications including sensitive metrology, ground state cooling of mechanical motion and slowing of light.

Cell manipulation by using integrated light driven on-chip actuator

Cell manipulation by using integrated light driven on-chip actuator

$Q$ Control of an Active AFM Cantilever With Differential Sensing Configuration

Microcantilevers featuring separate built-in actuation and displacement sensing capabilities allow effective and simple implementation of control methods, opening a pathway to achieving higher scan speeds in tapping-mode atomic force microscopy. Such active cantilevers are a significant milestone to eventually obtain video-rate on-chip atomic force microscopes (AFMs) that can even surpass the functionality and imaging speed of their macroscale counterparts at a significantly lower cost. In this brief, we present an active AFM cantilever with an on-chip actuator and two built-in displacement sensors, designed to be integrated into on-chip AFMs. The common feedthrough problem present in this type of architecture is addressed by a differential sensing configuration, and the revealed dynamics are used for the system identification. A positive position feedback controller is designed to actively tailor the $Q$ factor of the cantilever. The imaging performance of the microcantilever with and without $Q$ control is compared by attenuating the cantilever’s $Q$ factor from 177 to 15 using the feedback loop. A common artifact in high-speed scans, the parachuting effect, is mitigated, rendering higher imaging speeds achievable.

Self-contained on-chip fluid actuation for flow initiation in liquid cell transmission electron microscopy

Liquid cells for transmission electron microscopy enable the observation of liquid samples with nanometer resolution, but sample activity must often be triggered via external stimuli including liquid flow and mixing. Existing devices enable flow using specialized TEM holders and external pumping setups which limits technique accessibility. Here, a liquid cell with integrated MEMS valves and pumps is demonstrated with flow capabilities using an electrical-contact holder. On-chip electrochemical pumps and capillary burst valves allow for the injection of fluid from an integrated reservoir into an observation chamber using only electrical signals from a general microchip-sized TEM holder.

On-Chip Piezoelectric Actuation of Nanomechanical Resonators Containing a Two-Dimensional Electron Gas

The on-chip piezoelectric actuation is experimentally shown to be a suitable method for driving the resonant vibrations of AlGaAs/GaAs-based nanomechanical resonators containing a two-dimensional electron gas. Both flexural and torsional vibrations of 166 nm-thick cantilevers and doubly clamped beams can be driven using this method at room temperature. At least two points should be addressed when reducing the size of the piezoelectrically driven resonators. First, as shown in the paper, the parasitic attenuation of the driving electrical signal becomes the main factor limiting the actuation efficiency at the eigenfrequencies increased to the megahertz range due to the size reduction. Second, thin and relatively long bridge-like AlGaAs/GaAs-based resonators are prone to the Euler buckling instability caused by the longitudinal compressive stress. It is demonstrated that the buckling does not hinder the actuation at near-critical compression. However, a large super-critical compression can lead to a complete suppression of the piezoelectrically driven vibrations. A method to avoid this suppression is proposed.

Post-Release Deformation and Motion Control of Photonic Waveguide Beams by Tuneable Electrothermal Actuators in Thick SiO₂.

Photonic packaging, which includes high-precision assembly of photonic sub-systems, is currently a bottleneck in the development of commercially-available integrated photonic products. In the pursuit of a fully-automated, high-precision, and cost-effective photonic alignment scheme for two multi-channel photonic chips, this paper explores different designs of the on-chip electrothermal actuators for positioning mechanically-flexible waveguide structures. The final alignment goal is ∼100 nm waveguide to waveguide. The on-chip actuators, particularly for out-of-plane actuation, are built in a 16 μm-thick SiO photonic-material stack with 5 μm-thick poly-Si as an electrothermal element. A major challenge of out-of-plane positioning is a 6 μm height difference of the waveguides to be aligned, due to different built-up material stacks, together with a misalignment tolerance of 1 μm–2 μm from the pre-assembly (flip-chip) process. Therefore, the bimorph-actuator design needs to compensate this height difference, and provide sufficient motion to align the waveguides. We propose to exploit the post-release deformation of so-called short-loop bimorph actuator designs to meet these joint demands. We explore different design variants based on the heater location and the integration of actuator beams with waveguide beams. The actuator design (with 30 μm poly-Si and 900 μm SiO in length) has ∼8 μm out-of-plane deflection and is able to generate ∼4 μm motion, which meets the design goal.

Harmonically-Driven Snapping of a Micromachined Bistable Mechanism With Ultra-Small Actuation Stroke

In this paper, we study the snapping action of a micromachined bistable mechanism harmonically driven with an ultra-small actuation stroke, which is realized through the mode amplification in a two-degrees-of-freedom (2-DOF) vibration system using an on-chip electrostatic actuator. The micromachined bistable mechanism is based on a curved beam configuration. The dynamic response of the device is theoretically predicted with the harmonic balance method. Further, to demonstrate this proposed study, a microelectromechanical systems (MEMS) prototype device is designed, fabricated, and tested. In experiments, the forward and backward state switching actions of the prototype device are realized with actuation stroke smaller than $0.4~\mu \text{m}$ , while the traveling distance between the two states is about $18~\mu \text{m}$ . To the best of our knowledge, we demonstrate for the first time the state switching of a cured beam bistable mechanism using harmonic driving in a 2-DOF vibration system. This paper has potential in applications including MEMS switches and MEMS filters. [2017-0221]

Acoustic actuation of in situ fabricated artificial cilia

We present on-chip acoustic actuation of in situ fabricated artificial cilia. Arrays of cilia structures are UV polymerized inside a microfluidic channel using a photocurable polyethylene glycol (PEG) polymer solution and photomasks. During polymerization, cilia structures are attached to a silane treated glass surface inside the microchannel. Then, the cilia structures are actuated using acoustic vibrations at 4.6 kHz generated by piezo transducers. As a demonstration of a practical application, DI water and fluorescein dye solutions are mixed inside a microfluidic channel. Using pulses of acoustic excitations, and locally fabricated cilia structures within a certain region of the microchannel, a waveform of mixing behavior is obtained. This result illustrates one potential application wherein researchers can achieve spatiotemporal control of biological microenvironments in cell stimulation studies. These acoustically actuated, in situ fabricated, cilia structures can be used in many on-chip applications in biological, chemical and engineering studies.

An Open-Source, Programmable Pneumatic Setup for Operation and Automated Control of Single- and Multi-Layer Microfluidic Devices.

Microfluidic technologies have been used across diverse disciplines (e.g. high-throughput biological measurement, fluid physics, laboratory fluid manipulation) but widespread adoption has been limited in part due to the lack of openly disseminated resources that enable non-specialist labs to make and operate their own devices. Here, we report the open-source build of a pneumatic setup capable of operating both single and multilayer (Quake-style) microfluidic devices with programmable scripting automation. This setup can operate both simple and complex devices with 48 device valve control inputs and 18 sample inputs, with modular design for easy expansion, at a fraction of the cost of similar commercial solutions. We present a detailed step-by-step guide to building the pneumatic instrumentation, as well as instructions for custom device operation using our software, Geppetto, through an easy-to-use GUI for live on-chip valve actuation and a scripting system for experiment automation. We show robust valve actuation with near real-time software feedback and demonstrate use of the setup for high-throughput biochemical measurements on-chip. This open-source setup will enable specialists and novices alike to run microfluidic devices easily in their own laboratories.

Note: Guaranteed collocated multimode control of an atomic force microscope cantilever using on-chip piezoelectric actuation and sensing.

The quality (Q) factor is an important parameter of the resonance of the microcantilever as it determines both imaging bandwidth and force sensitivity. The ability to control the Q factor of multiple modes is believed to be of great benefit for atomic force microscopy techniques involving multiple eigenmodes. In this paper, we propose a novel cantilever design employing multiple piezoelectric transducers which are used for separated actuation and sensing, leading to guaranteed collocation of the first eight eigenmodes up to 3 MHz. The design minimizes the feedthrough usually observed with these systems by incorporating a guard trace on the cantilever chip. As a result, a multimode Q controller is demonstrated to be able to modify the quality factor of the first two eigenmodes over up to four orders of magnitude without sacrificing robust stability.

Bedside Immune Monitoring: An Automated Immunoassay Platform for Quantification of Blood Biomarkers in Patient Serum within 20 Minutes.

This Article presents an automated, compact, and self-contained system for sensitive quantitative detection of blood biomarkers. A disposable microfluidic chip, prefilled with biomarker-specific reagents and magnetic beads, can be processed fully automatically by a readout platform, enabling an immunoassay-based analysis with a processing time from sample incubation to signal analysis of 20 min. Novel concepts for on-chip vortexing of the magnetic beads and on-chip reagent storage and actuation were developed. A lens-free photodiode readout system represents a cost-efficient approach for detecting the chemiluminescent signal. IL-8 spiked serum samples were measured with a high reproducibility and a limit of detection of 2.05 pg·mL-1. The system was validated with undiluted serum samples collected from trauma patients at the intensive care unit. The developed platform demonstrated good correlation with the clinical reference method, and the clinical trajectory course of IL-8 could be sufficiently followed. With an automated assay approach and an easily adaptable protocol, this portable platform has the potential to be utilized as a universal instrument for analyzing proteins in small sample volumes (<25 μL) in point-of-care settings.

Multi-MHz micro-electro-mechanical sensors for atomic force microscopy

Silicon ring-shaped micro-electro-mechanical resonators have been fabricated and used as probes for dynamic atomic force microscopy (AFM) experiments. They offer resonance frequency above 10MHz, which is notably greater than that of usual cantilevers and quartz-based AFM probes. On-chip electrical actuation and readout of the tip oscillation are obtained by means of built-in capacitive transducers. Displacement and force resolutions have been determined from noise analysis at 1.5fm/√Hz and 0.4 pN/√Hz, respectively. Despite the high effective stiffness of the probes, the tip-surface interaction force is kept below 1 nN by using vibration amplitude significantly below 100pm and setpoint close to the free vibration conditions. Imaging capabilities in amplitude- and frequency-modulation AFM modes have been demonstrated on block copolymer surfaces. Z-spectroscopy experiments revealed that the tip is vibrating in permanent contact with the viscoelastic material, with a pinned contact line. Results are compared to those obtained with commercial AFM cantilevers driven at large amplitudes (>10nm).