IC-compatible Process Research Articles

Integrated MEMS Toroidal Transformer With Ni-Zn Ferrite Core for Power Supply on Chip

A miniature integrable transformer is an obstacle to the miniaturization of packaged power supply on chip (PwrSoC). This letter introduces a through-silicon via (TSV) high-aspect-ratio toroidal transformer manufactured using microelectro-mechanical systems and electroplating. The primary coil and secondary coil of the transformer are interleaved on the toroidal core cavity, which is entirely wrapped in silicon, and a 1.2 mm high toroidal Ni-Zn ferrite core is formed. A 15:15 turn transformer is fabricated with a compact coil size of Φ4.1 × 2 mm with an aspect ratio (ratio of TSV depth to diameter) of 20. Measurements show that it has an inductance of 105 to 115 nH in a high frequency range of 1 to 80 MHz and a coupling coefficient of ∼0.7 in the range of 1 MHz to >15 MHz. Compared to that of the transformer without the Ni-Zn ferrite core, the coupling coefficient of the toroidal transformer increases by 40% with an inductance increase of 20%. At a frequency of 14 MHz, the transformer has a maximum quality factor of 16.7. The small size, IC compatible manufacturing process and excellent performance at high-frequency of the transformer proposed, meet the further integrated and miniaturized needs of PwrSoC.

An emission stable vertical air channel diode by a low-cost and IC compatible BOE etching process.

Nanoscale air/vacuum channel devices have shown great potential in extreme environments, high speed and low power consumption applications. Progress in fabrication, structure and material optimization keeps emerging. However, it remains challenging to achieve a stable large current emission at low voltages, which limit the practical application of nanoscale air/vacuum channel devices. Here, a vertical structure consisting of two asymmetric flat emitters and a sub-100 nm air channel is proposed and fabricated by a low-cost and IC compatible BOE etching process. Typical diode characteristics have been demonstrated and controlled by the channel length. More importantly, emission currents up to several hundreds of microamp have been achieved in air with voltages lower than 2 volts and remain stable under sweep, fixed and periodic voltages. Along with the stable emission, a rise/fall time of 25 ns has been achieved for 1 MHz input signal. The present study provides an emission-stable nanoscale air channel diode with good manufacturing and integration possibilities, which can be an element for the future logic circuits of nanoscale air/vacuum channel electronics.

Spectroscopic and Electrical Characterizations of Low-Damage Phosphorous-Doped Graphene via Ion Implantation.

Development of n-/p-type semiconducting graphenes is a critical route to implement in graphene-based nanoelectronics and optronics. Compared to the p-type graphene, the n-type graphene is more difficult to be prepared. Recently, phosphorous doping was reported to achieve air-stable and high mobility of n-typed graphene. The phosphorous-doped graphene (P-Gra) by ion implantation is considered as an ideal method for tailoring graphene due to its IC compatible process; however, for a conventional ion implanter, the acceleration energy is in the order of kiloelectron volts (keV), thus severely destroys the sp2 bonding of graphene owing to its high energy of accelerated ions. The introduced defects, therefore, degrade the electrical performance of graphene. Here, for the first time, we report a low-damage n-typed chemical vapor deposition (CVD) graphene by an industrial-compatible ion implanter with an energy of 20 keV where the designed protection layer (thin Au film) covered on as-grown CVD graphene is employed to efficiently reduce defect formation. The additional post-annealing is found to heal the crystal defects of graphene. Moreover, this method allows transferring ultraclean and residue-free P-Gra onto versatile target substrates directly. The doping configuration, crystallinity, and electrical properties on P-Gra were comprehensively studied. The results indicate that the low-damaged P-Gra with a controllable doping concentration of up to 4.22 at % was achieved, which is the highest concentration ever recorded. The doped graphenes with tunable work functions (4.85-4.15 eV) and stable n-type doping while keeping high-carrier mobility are realized. This work contributes to the proof-of-concept for tailoring graphene or 2D materials through doping with an exceptional low defect density by the low energy ion implantation, suggesting a great potential for unconventional doping technologies for next-generation 2D-based nanoelectronics.

ZnO on nickel RF micromechanical resonators for monolithic wireless communication applications

On-chip integrability of high-Q RF passives alongside CMOS transistors is crucial for the implementation of monolithic radio transceivers. One of the most significant bottlenecks in back-end-of-line (BEoL) integration of MEMS devices on CMOS processed wafers is their relatively low thermal budget, which is less than that required for typical MEMS material deposition processes. This paper investigates electroplated nickel as a structural material for piezoelectrically-transduced resonators to demonstrate ZnO-on-nickel resonators with a CMOS-compatible low temperature process for the first time. Aside from the obvious manufacturing cost benefit, electroplated nickel is a reasonable substitute for polycrystalline or single crystal silicon and thin-film microcrystalline diamond device layers, while realizing decent acoustic velocity and moderate Q. Electroplated nickel has been already adopted by MEMSCAP, a multi-user MEMS process foundry, in its MetalMUMPs process. Furthermore, it is observed that a localized annealing process through Joule heating can be exploited to significantly improve the effective mechanical quality factor for the ZnO-on-nickel resonators, which is still lower than the reported AlN resonators. This work demonstrates ZnO-on-nickel piezoelectrically-actuated MEMS resonators and resonator arrays by using an IC compatible low temperature process. There is room for performance improvement by lowering the acoustic energy losses in the ZnO and nickel layers.

Filter of SSI-LED Light Using Thin Films

Recently, Kuo and Lin presented a new-type of solid state incandescent light emitting device (SSI-LED) that was made from a MOS structure with a high-k dielectric thin film, such as the Zr-doped HfO2 (ZrHfO) [1-3]. This kind of device emits the warp white light from the thermal excitation of nano-sized conductive paths surrounded by the dielectric film during the passage of a large current [4]. The emitted light covers the visible to near-IR wavelength range similar to that emitted from an incandescent light bulb [4]. The device was fabricated using the IC compatible process. Possible applications of the SSI-LED include displays, sensors, and in-chip optical interconnects [5]. For certain applications, such as the short distance optical interconnect, the wavelength has to be around 850-900 nm [67], which is within the wavelength range of the light emitted from the SSI-LED. It is also suitable for the light sensing using the Si diode [7]. A proper thin film light filter may be used for this purpose. In this paper, PECVD SiNx and a-Si:H thin films were examined for the light filtration of the light emitted from the SSI-LED made of the ZrHfO high-k dielectric. A 200 nm thick SiNx film was deposited on the dilute HF cleaned p-type Si (100) wafer and wet-etched into 250 µm diameter holes. A ZrHfO film was sputter-deposited on the substrate from a ZrHf (12/88 wt. %) target for 12 min in Ar/O2 (1:1) at 5 mTorr and 60 W. Then, an ITO film was sputter deposited on top of the ZrHfO film and wet etched into gate electrodes, which were connected to contact pads at the edge of the substrate through metal lines composed of Mo (200 nm)/Al (120 nm). The backside of the wafer was deposited with Mo to form the ohmic contact. The post metal annealing was done in a forming gas at 250°C for 5 min. The light emission spectrum of the SSI-LED was measured at the gate voltage (Vg ) of -20 V. Subsequently, the device was coated with a film of a 200 nm thick SiNx or a 6.5 nm thick a-Si:H deposited by PECVD. The spectrum of the light emitted from the same SSI-LED coated with the thin film was measured. Spectra of the same device with and without the filter were compared. Figure 1 shows the normalized light emission spectra of the SSI-LED before and after coating with the SiNx film. Before the SiNx coating, the light emission spectrum covers the wavelength range of 480 nm to 900 nm with the peak located at 700 nm. It is similar to spectra of typical SSI-LEDs without any filter [1-4]. However, when coated with the SiNx film, the shape of the spectrum changed. None of the light below 500 nm wavelength is detected. The spectrum contains two peaks at around 550 nm and 720 nm. The light above 750 nm wavelength drops, which becomes more obvious with the increase of the wavelength. The spectrum of the SiNx filtered SSI-LED is similar to the light transmission spectrum of the SiNx film [8]. The strong light absorption of SiNx at 600-650 nm and 900-1000 nm wavelength ranges contributes to the dual-peak spectrum in Fig. 1. Figure 2 shows the normalized light emission spectra of the SSI-LED before and after coating with an a-Si:H film. After coating with the a-Si:H film, the light emission spectrum shifted toward the long wavelength direction, i.e., from the peak of 700 nm to 750 nm. The intensity of the light in the 480 to 580 nm range dropped to zero. Previously, it was reported that the a-Si:H film strongly absorbed the short wavelength light in the 300 nm to 600 nm range [9]. Fig. 2 shows that the SSI-LED light below 650 nm is totally absorbed by the top a-Si:H film. In summary, the broad band light emitted from the SSI-LED can be filtered to a narrow wavelength range with a deposited thin film. [1] Y. Kuo and C.-C. Lin, APL, 102, 031117 (2013). [2] Y. Kuo and C.-C. Lin, ESSL, 2, Q59 (2013). [3] Y. Kuo and C.-C. Lin, SSE, 89, 120 (2013). [4] Y. Kuo, IEEE TED, 62, 3536 (2015). [5] Y. Kuo, ECS Tran., 54, 273 (2013). [6] D. A. B. Miller, IEEE Proc., 88(6), 728 (2000). [7] S. Radovanovic et al, High-Speed Photodiodes in Standard CMOS Technology, p. 24 (2006). [8] A. M. Perez et al, Opt. Eng., 45, 123801 (2006). [9] X. Li et al, Opt. Express, 21, A677 (2013). Figure 1

FBAR-on-diaphragm type electro-acoustic resonant micro-accelerometer: a theoretical study

We presented a theoretical study of the performance of a novel FBAR-on-diaphragm sensor-head structure for the FBAR-based electro-acoustic resonant micro-accelerometer. This structure overcomes disadvantages in the FBAR-beam structure for its limited cantilever beam thickness, and deficiencies in the embedded-FBAR structure for its complex micro-fabrication process. Its elastic diaphragm is made of silicon dioxide (SiO2)/silicon nitride (Si3N4) bilayer film, which is not only more susceptible to the IC compatible integration process for the Si-based microstructure and the FBAR, but also improves sensitivity and temperature stability of the BAW accelerometer. FBAR-on-diaphragm type BAW accelerometer integrates the acceleration sensing structure, i.e., the SiO2/Si3N4 bilayer diaphragm and the Si proof-mass, with the AlN FBAR electro-acoustic transducer. Preliminary performance analysis on FBAR-on-diaphragm type BAW accelerometer suggests that the FBAR-on-diaphragm structure is feasible. We obtained modal frequencies of the FBAR-on-diaphragm structure and stress distribution of the diaphragm under 0---100 g acceleration loads through the finite element modal analysis and static simulation, Applying the calculated maximum stress to the piezoelectric film in FBAR for qualitative analysis, and combining the dependency of elastic coefficient on stress in the Wurtzite AlN film calculated with the first-principle method, we roughly predicted the maximum elastic coefficient variation in the Wurtzite AlN film under different acceleration load. With the help of the RF simulation software ADS, we changed the longitudinal wave velocity corresponding to the elastic constants with variant acceleration loads. By comparing the resulted resonant frequencies of the sensor head without and with different acceleration loads, we qualitatively characterized its frequency shift and sensitivity. In our study, we gave further analysis of the simulation results. It reveals that the first-order modal frequency of the SiO2/Si3N4 circular diaphragm is quite far away from the higher ones, which means less cross modal coupling. It also reveals that under the acceleration load, its resonant frequency with a quite linear acceleration---frequency shift characteristic will up-shift with the sensitivity of several KHz/g.

X-Ray Absorption Spectra and Self-Bias Ferromagnetic Resonance of FeCoB Films Prepared by Composition Gradient Sputtering

Microwave soft magnetic films (SMFs) are key materials, which can effectively miniaturize and multifunctionalize the electromagnetic components and devices, such as filters, phase shifters, thin film wireless inductors, magnetic recording write heads, antennas, etc.1, and reduce their occupation area in microwave monolithic integrated circuit (MMIC) boards. Modern electronic products are heading towards high density, high-frequency, frequency tunability, lightweight and low energy consumption, etc., which give rise to increasing demands for microwave SMFs. Microwave SMFs should have higher ferromagnetic resonance frequency (f FMR ), high permeability, and are to be fabricated in an IC compatible process. Metallic soft magnetic films exhibit special advantages in MMIC devices since they have higher 4πM S and permeability, and good compatibility with the IC fabrication process. Therefore, self-biased metallic SMFs prepared at IC compatible process have drawn an increasing attention2.

A Solid-State Thin-Film Incandescent Light-Emitting Device

A new type of solid-state thin-film white light-emitting device has been reviewed and discussed. Light is emitted due to thermal excitation of the nano-sized conductive paths formed after the dielectric breakdown of the amorphous metal oxide thin film deposited on a silicon wafer. The mechanism of light emission, optical characteristics, reliability, driving methods, and efficiency are discussed. The complete device is made of the IC-compatible materials and process.

Solid State Incandescent Light Emitting Device Made of WOx Embedded Zr-Doped HfO2 High-k Stack on Si

The phenomenon of white light emission from the WOx embedded Zr-doped HfO2 high-k dielectric MOS device has been investigated. The embedding of the WOx layer into the high-k stack increased the breakdown voltage due to the larger physical thickness. Light was emitted from many discrete nano dots due to thermal excitation of conductive paths formed from the dielectric breakdown process. The inclusion of the W component in the conductive path enhanced the emission of the red to IR portion of the light. The light intensity corresponds to the current density, which increases with the diving voltage. Judged from the light emission mechanism and optical properties, the light emission phenomenon is close to the blackbody emission. This kind of device can be applied to many products to take the advantage of its unique optical and thermal characteristics as well as the IC compatible fabrication process.

Driving ferromagnetic resonance frequency of FeCoB/PZN-PT multiferroic heterostructures to Ku-band via two-step climbing: composition gradient sputtering and magnetoelectric coupling.

RF/microwave soft magnetic films (SMFs) are key materials for miniaturization and multifunctionalization of monolithic microwave integrated circuits (MMICs) and their components, which demand that the SMFs should have higher self-bias ferromagnetic resonance frequency fFMR, and can be fabricated in an IC compatible process. However, self-biased metallic SMFs working at X-band or higher frequency were rarely reported, even though there are urgent demands. In this paper, we report an IC compatible process with two-step superposition to prepare SMFs, where the FeCoB SMFs were deposited on (011) lead zinc niobate–lead titanate substrates using a composition gradient sputtering method. As a result, a giant magnetic anisotropy field of 1498 Oe, 1–2 orders of magnitude larger than that by conventional magnetic annealing method, and an ultrahigh fFMR of up to 12.96 GHz reaching Ku-band, were obtained at zero magnetic bias field in the as-deposited films. These ultrahigh microwave performances can be attributed to the superposition of two effects: uniaxial stress induced by composition gradient and magnetoelectric coupling. This two-step superposition method paves a way for SMFs to surpass X-band by two-step or multi-step, where a variety of magnetic anisotropy field enhancing methods can be cumulated together to get higher ferromagnetic resonance frequency.

Single-Grain Si Tfts Fabricated on a Precursor from Doctor-Blade Coated Liquid-Si

In the application of display, Si TFTs is superior than organic TFTs and metal oxide TFTs in the sense of carrier mobility, reliability and traditional IC process compatibility. However, the difficulty of achieving single crystalline Si limits the application of Si TFTs. In this paper, we would like to present a low-temperature approach for manufacturing single-grain Si TFTs on a precursor from doctor-blade coated liquid-Si on flexible polyimide substrate, with the carrier mobility of 460 cm2/Vs and 121 cm2/Vs, for electrons and holes respectively.Pure cyclopentasilane is used as liquid-Si, and it was coated using doctor-blade method, and polymerized under the UV lamp. According to [1], polysilane was formed after polymerizing the solution of cyclopentasilane and toluene. After an annealing process at 350 °C, an a-Si precursor was formed (see Fig. 1). A XeCl laser with the wavelength of 308 nm was used for the crystallization of the a-Si precursor, and thanks to the special cavity structures called the grain-filters, which are 110 nm width by 700 nm depth, underneath the a-Si layer, Si single grains were formed[2] (see Fig.2). A top-gated transistor was fabricated using the IC-compatible process of ICP gate oxide growth (250 °C), PECVD TEOS oxide (350 °C), Al gate and contact pads formation, self-aligned source-drain dopant ion-implantation and laser activation of the dopants (room temperature). The process temperature was so low that the devices were fabricated on top of flexible polyimide substrate. At the end of the process, all the devices were peeled off from the supporting Si wafer to a PEN foil and become flexible (Fig. 5).The devices show transfer characteristics with high on-off ratio and high carrier mobility, 420 cm2/Vs for electrons and 121 cm2/Vs for the holes (Fig. 3). After peeling off from the Si wafer, the devices could function until a bending diameter of 6 mm (Fig.4). To restrain the mobility degradation during the bending, a double-sided polyimide structure was investigated.[1] T. Shimoda, Y. Matsuki, M. Furusawa, T. Aoki, I, Yudasaka, H. Tanaka, H. Iwasawa, D. Wang, M. Miyasaka and Y. Takeuchi, Nature 440, 6, 2006, 783-786[2] R. Ishihara, P.C. van der Wilt , B.D. van Dijk , A. Burtsev , J.W. Metselaar and C.I.M. Beenakker, Thin Solid Film 427, 2003, 77-85

Design, fabrication and characterization of infrared LVOFs for measuring gas composition

This paper presents the design, fabrication and characterization of a linear-variable optical-filter (LVOF) that will be used in a micro-spectrometer operating in infrared (IR) for natural gas composition measurement. An LVOF is placed on top of an array of detectors and transforms the optical spectrum into a lateral intensity profile, which is recorded by the detectors. The IR LVOF was fabricated in an IC-compatible process using a photoresist reflow technique, followed by transfer etching of the photoresist into the optical resonator layer. The spectral range between 3 to 5 µm contains the absorption peaks for hydrocarbons, carbon-monoxide and carbon-dioxide. The resulting optical absorption is utilized to measure the gas concentrations in a sample volume. Two LVOF structures were designed and fabricated on silicon wafers using alternate layers of sputtered silicon and silicon-dioxide as the high- and low- refractive index materials. These filters consist of a Fabry–Pérot resonator combined with a band-pass filter designed to block out-of-band transmissions. Finally, the filters were fully characterized with an FTIR spectrometer and showed satisfactory agreement with the optical thin-film simulations. The characterization showed a spectral resolution of 100 nm, which can be further improved with signal processing algorithms. This method makes it possible to fabricate small and robust LVOFs with high resolving power in the IR spectral range directly on the detector array chip.

Process development of an all-silicon capacitive accelerometer with a highly symmetrical spring-mass structure etched in TMAH + Triton-X-100

This paper reports a fabrication process of a capacitive microelectromechanical system (MEMS) accelerometer with a highly symmetrical spring-mass structure for the high device performance, which is composed of eight springs and a central mass. The sandwich accelerometer is constituted by top layer, middle layer and bottom layer. The suspended spring-mass structure in the middle silicon layer is formed simply by double thermally grown oxide layers and the mask–maskless wet anisotropic etching, avoiding the generally adopted deep-groove photolithography when fabricating the thin spring. Moreover, the gap between electrodes can be determined by the thickness of the oxide layer in this process. The surfactant-modified TMAH is selected as the etchant because it not only provides the minimum undercutting at the mass corner, thus saving much space of the compensation parts, but also allows the good control of spring thickness at the low etch rate. The spring shape evolution during etching in surfactant-modified TMAH is simulated and the obtained rhombic cross-section has the advantage of easily identifying the thickness of the spring from its width according to their crystal orientation relation. The three silicon layers are bonded through silicon fusion bonding (SFB) at temperature >1000°C to relax surface stresses that could be present in the material prior bonding. Preliminary test result shows the sensitivity of 60mV/g with good linearity of R2=0.99979 in a closed-loop interface circuit. The advanced accelerometer performance could be expected due to the symmetrical structure, the large proof mass, controllable spring shape, the narrow uniform capacitive gap, and the IC-compatible process.

Post Deposition Annealing Temperature Effect on White-Light Emitting of WOx Thin Film Stack on Si

Post Deposition Annealing Temperature Effect on White-Light Emitting of WOx Thin Film Stack on Si

Electrohydrodynamic Microfabricated Ionic Wind Pumps for Thermal Management Applications

This work demonstrates an innovative microfabricated air-cooling technology that employs an electrohydrodynamic (EHD) corona discharge (i.e., ionic wind pump) for electronics cooling applications. A single, microfabricated ionic wind pump element consists of two parallel collecting electrodes between which a single emitting tip is positioned. A grid structure on the collector electrodes can enhance the overall heat-transfer coefficient and facilitate an IC compatible batch process. The optimized devices studied exhibit an overall device area of 5.4 mm × 3.6 mm, an emitter-to-collector gap of ∼0.5 mm, and an emitter curvature radius of ∼12.5 μm. The manufacturing process developed for the device uses glass wafers, a single mask-based photolithography process, and a low-cost copper-based electroplating process. Various design configurations were explored and modeled computationally to investigate their influence on the cooling phenomenon. The single devices provide a high heat-transfer coefficient of up to ∼3200 W/m2 K and a coefficient of performance (COP) of up to ∼47. The COP was obtained by dividing the heat removal enhancement, ΔQ by the power consumed by the ionic wind pump device. A maximum applied voltage of 1.9 kV, which is equivalent to approximately 38 mW of power input, is required for operation, which is significantly lower than the power required for the previously reported devices. Furthermore, the microfabricated single device exhibits a flexible and small form factor, no noise generation, high efficiency, large heat removal over a small dimension and at low power, and high reliability (no moving parts); these are characteristics required by the semiconductor industry for next generation thermal management solutions.

Integrated flexible parylene-based inductor with magnetic core for wireless power transmission system

In this paper, flexible parylene-based MEMS inductors were designed, fabricated and analysed. A magnetic core was added in the centre of spiral coil in order to further enhance the performance of the inductor. FeNi alloy was chosen as the magnetic material due to its relatively high permeability. Parylene was used as substrate and insulation material due to its good bio-compatibility and flexibility. The performance of inductors was simulated in Ansoft HFSS. When the core radius increased from 800 μm to 1200 μm, the inductance was increased by 167% and the quality factor was increased by 20%. The inductors were fabricated using standard IC compatible MEMS fabrication process. Copper coils and magnetic cores were fabricated by electrodeposition technique. We also tested the performance of our fabricated inductors. When adding the magnetic core, the inductance was improved by 125% (from 44 nH to 100 nH) and the peak quality factor was improved by 18% (from 4.62 to 5.45). When the core radius increased from 800 μm to 1200 μm, the inductance was improved by 67% (from 173 nH to 289 nH) and the peak quality factor was improved by 83% (from 1.20 to 2.19). Finally, the fabricated inductors were tested in our experimental system. The minimum of transmission attenuation was –32 dB at 29 MHz.

Post Deposition Annealing Temperature Effect on White-light Emitting of Sputter Deposited Zr-doped HfO2 Thin Film

ABSTRACTThe warm white light emission from the MOS capacitor containing the Zr-doped HfO2 high-k thin film on a p-type Si wafer under various post deposition annealing temperatures has been investigated. The light intensity is affected by the annealing temperature and the magnitude of the stress voltage. The annealing temperature changes the defect density and the physical thickness of the high-k stack. The high stress voltage induces the strong light emission because of the passage of a large current through the conductive path. The broad band emission spectrum covers the visible and near IR wavelength range with a large color rendering index. This new light emission device has a very long lifetime of > 1,000 hours at the atmosphere without a protection layer. The device is made of the IC compatible material and fabrication process, which favors the application over a wide range of products.

Factors Affecting Light Emission from Solid State Incandescent Light Emitting Devices with Sputter Deposited Zr-Doped HfO2 Thin Films

The light emission characteristics of a new type of solid state light emitting device, which is based on the thermal excitation of conductive paths formed in the Zr-doped HfO2 high-k dielectric stack, have been investigated with respect to the fabrication process, film properties, the device driving method, and the lifetime. The emission spectrum covers the visible to the near IR wavelength range with a high color rendering index of 98.1. The light intensity increases with the increase of the post deposition annealing temperature due to changes of the film thickness and defect density. It also increases with the increase of the magnitude of the driving voltage because of the enhancement of the thermal excitation of the conductive path. The light emission intensity decreases with the reduction of the duty cycle in the pulsed driving condition but the emission spectrum remains in the same wavelength range. This device has a very long lifetime of >2,800 hours in the atmosphere. This new device is made of the IC compatible material and fabrication process, which favors the application in a wide range of products.

Parallel-plate lab-on-a-chip based on digital microfluidics for on-chip electrochemical analysis

This paper describes an electrowetting on dielectric (EWOD) digital microfluidic-based lab-on-a-chip (LOC) integrated with on-chip electrochemical microsensor by IC compatible fabrication process, and its application for the entire online biosensing process capable of fully automatic analysis for ferrocenemethanol (FcM) and dopamine (DA). In this work, we made full use of the parallel-plate structure of the EWOD digital microfluidic device to fabricate the microfluidic module on the bottom plate and the three-microelectrode-system-integrated electrochemical cell together with patterned ground electrode on the top plate. The proposed LOC possesses the multifunction of: (1) creating, merging and transporting of microliter-level sample droplets, (2) online biosensing, and (3) droplets recycling. The three-electrode-integrated microsensor not only reveals a sensitive electrochemical detection for FcM in a wide concentration range (10 µM–1.0 mM), but also shows good stability, selectivity and reproducibility for surface-controlled detection of DA. The calibration of DA was linear for concentration from 1.0 to 50.0 µM with a high sensitivity of 2145 nA µM−1 cm−2 (R2 = 0.9933) and estimated detection limit of 0.42 µM (signal/noise ratio of 3). This work shows the promise of state-of-the-art digital microfluidic biosensors for fully automatic online bioanalysis in a future LOC to perform on-chip biomedical protocols in vitro diagnostic assays.

Integrated Piezoresistive Force and Position Detection Sensors for Micro-Handling Applications

This paper presents two integrated piezoresistive sensors capable of detecting simultaneously both the contact force and the contact position of a micro-object in micro-handling applications. The first sensor detects the 1-D contact position in vertical direction along a contact surface. The second sensor extends the sensing principle and detects the contact position on a 2-D contact surface. The devices combine the outputs of two groups of piezoresistors in Wheatstone bridge configurations, allowing the computation of the contact force and the contact position. The sensors are fabricated with an IC-compatible process and can be integrated in micro-handling tools such as micro-grippers. The two devices are characterized by applying forces onto the contact surface at pre-defined positions. With an applied contact force ~ 1 mN, the first sensor has a force resolution of 1 μN and a vertical position detection accuracy of 2-3 μm. The estimated force range detectable is 3 mN and a sensitivity of 2.8 V/N is obtained with an effective supply voltage of 177 mV across the Wheatstone bridge. The second sensor has a force detection range up to 3 mN with a resolution of 20 μN under a measured noise of 30 μV. The theoretical spatial resolution is ~ 5μm in both x and y directions with a contact force of 1 mN. The devices are designed to handle micro-objects with sizes of 25-250 μm. The concept and the principle of the device are not limited to applications in micro-grippers and can be used in other micro-handling tools.