Paul Rainey

Characterization of masking materials for deep glass micromachining

In this paper the characterization of different masking materials for the fabrication of flow channels or thin diaphragms in aluminosilicate glass substrates (Corning 1737) is presented. Materials such as photoresist, polysilicon and gold were investigated with concentrated hydrofluoric acid, HF 48% used as an isotropic etchant. The use of single material masks restricts the useable etch depth to less than 250 µm. Surface and material imperfections result in weaknesses in the masking layer and subsequent penetration by the etchant. An etch depth of greater than 300 µ mw as achieved using a combination of thick SU-8 photoresist and polished polycrystalline silicon as the masking material. The two materials act as double protection to the glass substrate and the etch depth obtained is approximately three to six times larger than those published for standard photoresist or SU-8 etch mask.

A microfluidic anti-Factor Xa assay device for point of care monitoring of anticoagulation therapy.

The development of new point of care coagulation assay devices is necessary due to the increasing number of patients requiring long-term anticoagulation in addition to the desire for appropriate, targeted anticoagulant therapy and a more rapid response to optimization of treatment. The majority of point of care devices currently available for hemostasis testing rely on clot-based endpoints which are variable, unreliable and limited to measuring only certain portions of the coagulation pathway. Here we present a novel fluorescence-based anti-Factor Xa (FXa) microfluidic assay device for monitoring the effect of anticoagulant therapy at the point of care. The device is a disposable, laminated polymer microfluidic strip fabricated from a combination of hydrophobic and hydrophilic cyclic polyolefins to allow reagent deposition in addition to effective capillary fill. Zeonor was the polymer of choice resulting in low background fluorescence (208.5 AU), suitable contact angles (17.5°± 0.9°) and capillary fill times (20.3 ± 2.1 s). The device was capable of measuring unfractionated heparin and tinzaparin from 0-0.8 U ml(-1) and enoxaparin from 0-0.6 U ml(-1) with average CVs < 10%. A linear correlation was observed between the device and the fluorescent assay in the plate for plasma samples spiked with UFH, with an R(2) value of 0.99, while correlations with tinzaparin and enoxaparin resulted in sigmoidal responses (R(2) = 0.99). Plasma samples containing UFH resulted in a linear correlation between the device and a standard chromogenic assay with an R(2) value of 0.98, with both LMWHs resulting in sigmoidal relationships (R(2) = 0.99).

Investigation of germanium implanted with hydrogen for layer transfer applications

The technology for thin Ge layer transfer by hydrogen ion-cut process is characterised in this work. Experiments were carried out to determine suitable hydrogen ion implantation doses in germanium for the low temperature ion cut process by examining the formation of blisters on implanted samples. Raman and Spreading Resistance Profiling (SRP) have been used to analyse defects in germanium caused by hydrogen implants. Bevelling has been used to facilitate probing beyond the laser penetration depth. Results of Raman mapping along the projection area reveal that after post implant annealing at 400 °C, some crystal damage remains, while at 600 °C, the crystal damage has been repaired. SRP shows that some amount of hydrogen acceptor states (~1Î1016 acceptors/cm2) remain after 600 °C. These are thought to be vacancy-related point defect clusters.

Flow rate measurement via conductivity monitoring in micro-fluidic devices

This paper investigates methods of flow rate quantification in micro- fluidic devices, using electrodes to measure the conductivity of solution. Conductivity changes occur when liquid flow causes movement of the boundary between two solutions of differing conductivity. The fabrication technology for the micromachined silicon structures is based on anisotropic etching and anodic bonding to glass. The silicon processing is simplified by using a single-mask process, whereby 9 - 15 mm long, 50 - 100 micrometers wide capillaries and access through-holes are created with a single etch step. Thin film gold electrodes patterned on the glass provide contact with the liquid in the capillary. The current monitoring method, used in capillary electrophoresis, is employed to determine conductance-time waveforms during electroosmotic pumping. The waveforms for silicon based devices are distorted due to oxide capacitance and the profiles of the ends of the channel. The transitions are much more linear for reference devices formed using standard glass capillary tubing. Electrical models are developed for the devices and these are used to determine flow velocities and hence volume flow rates of liquid.

Micro-Raman and Spreading Resistance Analysis on Beveled Implanted Germanium for Layer Transfer Applications

D Micro-Raman and Spreading Resistance Analysis on Beveled Implanted Germanium for Layer Transfer Applications Paul Rainey,* Joanna Wasyluk, Tatiana Perova, Richard Hurley, Neil Mitchell, David McNeill, Harold Gamble,* and Mervyn Armstrong School of Electrical Engineering and Computer Science, Northern Ireland Semiconductor Research Center, The Queen’s University of Belfast, Belfast, BT9 5AH, Northern Ireland, United Kingdom Department of Electronic and Electrical Engineering, University of Dublin, Trinity College, Dublin 2, Ireland

Germanium on sapphire

This paper explores the potential of germanium on sapphire (GeOS) wafers as a universal substrate for System on a Chip (SOC), mm wave integrated circuits (MMICs) and optical imagers. Ge has a lattice constant close to that of GaAs enabling epitaxial growth. Ge, GaAs and sapphire have relatively close temperature coefficients of expansion (TCE), enabling them to be combined without stress problems. Sapphire is transparent over the range 0.17 to 5.5 μm and has a very low loss tangent (α) for frequencies up to 72 GHz. Ge bonding to sapphire substrates has been investigated with regard to micro-voids and electrical quality of the Ge back interface. The advantages of a sapphire substrate for integrated inductors, coplanar waveguides and crosstalk suppression are also highlighted. MOS transistors have been fabricated on GeOS substrates, produced by the Smart-cut process, to illustrate the compatibility of the substrate with device processing.

A fully integrated microfluidic device for point of care monitoring of antithrombotics

The simplicity and efficiency of point of care diagnostics have revolutionised patient care. Current methods for measuring hypercoagulability often require trained technicians, large blood volumes, and result in long turnaround times. Standard testing for hypercoagulable disorders is performed in the central laboratory using automated coagulation analysers. However the trend is moving towards the development and implementation of point of care testing, as a result of the ever increasing number of patients on antithrombotic therapy. We present a novel microfluidic device and assay for monitoring the effect of two anticoagulants, unfractionated heparin (UFH) and low molecular weight heparin (LMWH). The assay is based on the anti-Xa assay principle but uses fluorescence detection. Our device is a disposable laminate microfluidic strip, fabricated from the cyclic polyolefin (COP), Zeonor®, which is extremely suitable for application to fluorescent device platforms. We present data on the execution of the anti-Xa assay in this microfluidic format, demonstrating that the assay can be used to measure both UFH and LMWH in human plasma samples from 0 to 1 U mL−1, with a rapid result obtained within 30–60 seconds.

Germanium Bonding to AL2O3

Germanium has attractive properties such as high carrier mobility, compatibility with high-K dielectrics, lattice matched for GaAs growth. Germanium on insulator (GOI)(1,2) offers the advantages of germanium and combines them with those of silicon on insulator (SOI). In this work germanium bonding to alumina (AL2O3) is discussed. This platform has added advantages such as thermal matching between the AL2O3 and the germanium substrates, allowing temperatures above 600C to be used without cracking occurring in Ge layer. AL2O3 also offers lower substrate losses than standard SOI and better crosstalk suppression(3). Single crystal AL2O3 , in the form of sapphire, and fine grain AL2O3 have been investigated as possible handle substrates. The single crystal AL2O3 layer employed was Cplane sapphire with an epi ready polished surface. The thickness of the sapphire was 500μm and the surface roughness was measured by white light interferometery to be 0.85nm. The germanium substrates were Umicore produced (100) substrates 500μm thick. Figure 1 shows the bond interface of a silicon dioxide coated germanium substrate bonded to sapphire after the bonded pair had received a bond strengthening anneal at 500 C for 120mins. This image is an optical photograph taken through the transparent sapphire substrate. The thermal coefficient of expansion match between the sapphire substrate and germanium allows higher temperature annealing without cracking of the germanium layer. Sapphire substrates can be expensive costing up to

SPICE modelling of liquid capacitance in micromachined silicon capillaries

200 /substrate. However fine grain AL2O3 which has the same substrate advantages has a lower cost. Producing a bondable fine grain alumina substrate would allow a more cost effective germanium on AL2O3 platform to be established. In this work fine grain AL2O3 (grain size < 1μm ) having a measured rms surface roughness of 11nm was used. Figure 2 shows a white light interferometer image of the substrate surface. The surface finish in its current state is not suitable for bonding. However, by introducing an interfacial layer that can be readily polished a suitable bonding surface can be achieved. Polycrystalline silicon is used in this work. A 0.5μm polysilicon layer was deposited at 620C onto the fine grain AL2O3 . CMP technology was used to produce a smooth surface finish. In order to test the bondability of the surface finish, room temperature bonding was performed between the polysilicon coated AL2O3 handle substrate and a thermally oxidised silicon substrate. As the fine grain AL2O3 is not transparent, IR imaging was used to inspect the bond interface. Figure 3 is an IR image of the bond interface. This demonstrates that a bondable AL2O3 substrate can be achieved. Germanium bonding to the polysilicon coated AL2O3 layer was attempted. The germanium was chemically treated with acetone and methanol followed by cyclic HF/DI water cleaning and dilute NH4OH surface passivation(4). The AL2O3 substrate received standard silicon based cleaning. A scanning acoustic micrograph of the room temperature bond is shown in figure 4. As can be seen from figure 4, successful bonding can be achieved between the germanium and fine grain alumina substrate.

A novel microfluidic anti-factor Xa assay device for monitoring anticoagulant therapy at the point-of-care

This paper investigates modeling of the conductance of liquid in a microchannel, using SPICE. When more than one liquid is present, conductance monitoring is an effective technique to measure electroosmotic flow rates. In micromachined silicon capillaries, the technique is hampered by the capacitance that exists between the bulk fluid and the silicon substrate, and leakage currents due to the thin insulating oxide layer. A SPICE model is used to simulate conductance waveforms, by using MOS transistors to model the time dependant resistance of the channel. The simulation results are used to determine the capacitance and explain the conductance waveforms measured for micromachined silicon channels.