Graham J. Ensell

Design and theoretical evaluation of a novel microfluidic device to be used for PCR

The design of a novel, microfluidic chip with an integrated micro peristaltic pump and chambers for DNA amplification is described. This chip contains three reaction chambers stable at 90 °C, 72 °C and 55 °C for PCR amplification, a bi-directional peristaltic pump and optical integrated detection of the droplet. A reactant droplet is to be introduced into the device, pumped back and forth between the chambers by the micro peristaltic pump for sample processing. The static behaviour of the micro pump was modelled theoretically in order to evaluate the optimal dimensions for the pump membranes and to obtain the maximum flow rate. Thermal analysis by the finite element method was performed to optimize the location of the heaters and the temperature uniformity over the three reaction chambers. Transient thermal analysis indicates that the reactant droplet can be heated/cooled in the proposed device in less than 1 s to achieve the desired temperatures.

Characterization of a highly sensitive ultra-thin piezoresistive silicon cantilever probe and its application in gas flow velocity sensing"

We present a highly sensitive ultra-thin micromachined silicon cantilever beam with an integrated strain gauge on its root for optimizing piezoresistive readout. The mechanical characteristics and electrical readout of the cantilever beam, such as spring constant, resonant frequencies and piezoresistive sensitivity, are theoretically given from the derived formulae or from finite element modeling. The results of characterization show reasonably good agreement between the experimental results and the theoretical values. As one of the applications, for the first time the fabricated silicon cantilever beams have been applied to measure airflow velocity distribution in a steel pipe with an inner diameter of 7.0 mm. The experimental piezoresistive sensitivity (ΔR/R)/y(0) is in the range of 0.23–2.89 × 10−6 nm−1 in the beam bending tests, and the experimental flow sensitivity (ΔR/R)/Vgas2 is in the range of 0.652–4.489 × 10−5 (m s−1)−2 in the airflow velocity tests. The experimental detectable minimum airflow velocity is 7.0 cm s−1, which is comparable to that of a hot wire anemometer.

Free standing single-crystal silicon microstructures

Micromachined structures of single-crystal silicon have been fabricated with a view to developing them for a number of potential uses. The structures which are fabricated in (111) orientation silicon are undoped thus permitting the incorporation of active circuit elements in the structures themselves. Moreover no high temperatures, applied voltages or long etch times are used in the fabrication sequence, thereby simplifying the task of integration with circuit processes. The potential uses of these structures include photodiodes with high speed and efficiency, accelerometers, or structures for stress or thermal isolation.

Fabrication and test of thermal vertical bimorph actuators for movement in the wafer plane

We have fabricated thermal actuators based on vertical bimorphs, which consist of silicon beams side-coated with aluminium. When they are heated by an electrical current they bend like a bimetal and produce movement in the wafer plane. The fabrication process is based on silicon-on-insulator substrates and uses standard silicon micromachining techniques combined with a special aluminium sidewall deposition process. The displacement has been measured as a function of the input power and the results have been compared with an FEA-simulation.

A high efficiency input/output coupler for small silicon photonic devices

Coupling light from an optical fibre to small optical waveguides is particularly problematic in semiconductors, since the refractive index of the silica fibre is very different from that of a semiconductor waveguide. There have been several published methods of achieving such coupling, but none are sufficiently efficient whilst being robust enough for commercial applications. In this paper experimental results of our approach called a Dual-Grating Assisted Directional Coupler, are presented. The principle of coupling by this novel method has been successfully demonstrated, and a coupling efficiency of 55% measured.

Development of small silicon modulators in silicon-on-insulator (SOI)

Silicon-based optical modulators are expected to be important components in some optical networks. The optical modulation mechanism can be achieved either via the plasma dispersion effect, or by thermal means. Both are relatively slow processes when utilized in large (multi micron) waveguide structures, which researchers tend to concentrate on for ease of coupling. Using large waveguide structures limits the operating speed and hence excludes the applicability of these devices in areas where higher speeds are required. This limitation could be overcomed by using smaller waveguides (of the order of 1Rm). In this paper, we present the basic operating mechanism, design, and fabrication details of an optimum three terminal p-i-n diode based optical phase modulator based on Silicon-On-Insulator (501). The device was optimised via electrical and optical modeling and is predicted to operated at 1 .3GHz with a power reduction of900%, as compared to previously published designs.

Thick oxide pMOSFET dosimeters for high energy radiation

Abstract This work examines the response of pMOSFET dosimeters to ionizing radiation. The dosimeters were fabricated with gate oxides having a range of thicknesses varying from 0.69 μm for the thinnest oxide up to 2.3 μm for the thickest oxide. In separate experiments the dosimeters were irradiated by 60Co γ-rays and linac X-rays both with biassed and unbiassed gates. The effects on transistor characteristics were measured and analysed to show the relative contributions to the shift in the threshold voltage from trapped charge in the oxide and charges trapped at the silicon-silicon dioxide interface.

Time constant and lateral resonances of thermal vertical bimorph actuators

Thermal vertical bimorph actuators consist of silicon beams side-coated with aluminium. Upon heating they bend like a bimetal and produce movement in the wafer plane. We have measured the time constant describing the deflection response of the actuator to input pulses. Depending on the dimensions of the actuator, the time constant ranges from 0.5 ms to 3.8 ms. Lateral resonances of the first mode have been measured using thermal excitation and are found to be between 20 and 85 kHz.

Integrated diode detector and optical fibres for in situ detection within micromachined polymerase chain reaction chips

This paper reports on the design, fabrication, assembly and testing of a micromachined polymerase chain reaction (PCR) system with pigtailed fibre optics. Two major designs have been fabricated and tested. The first design uses two optical fibres, one for the projection of light into the chamber and the other for the collection of the light emitted by a fluorescent dye in the reaction chamber. The second design employs a single optical fibre for the delivery of light into the PCR chamber, with light now being detected using a photodiode integrated into the base and walls of the reaction chamber within the PCR chip. Tests carried out on both systems have produced promising results.

Fabrication of improved piezoresistie Si cantilever probes for the atomic force microscope

Abstract This paper describes an improved design for a monolithic silicon atomic force microscope (AFM) probe using piezoresistive sensing. The probe is V shaped, with a sharp tip at the free end and two piezoresistors at the root, and is fabricated using silicon-on-insulator (SOI) starting material. The maximum sensitivity of the AFM probe is measured to be 4.0(± 0.1) × 10 −7 A −1 , which is larger than that of the previous parallel-arm piezoresistive AFM probe. The measured results are in reasonable agreement with the values predicted by theory. The minimum detectable force and minimum detectable deflection of the AFM probes are predicted to be 1.0 × 10 −10 N and 0.29 A r.m.s. , respectively, using a Wheatstone bridge arrangement biased at a voltage of ± 5 V and bandwidth of 10 Hz–1 kHz.