We report on the fabrication of a flexible pressure sensitive device based on near-field coupling between silver nanoparticles and an underlying conductor. Visually apparent colour changes can be realized with minimal change in separation owing to the high fields localized to the particle's surface. The use of soft and compliant materials enables actuation of the device at low strain.

The detection of DNA hybridization using fieldeffect transistors (BioFETs) has attracted attention recently [1]. A model has been developed [2-3] to estimate threshold voltage shifts obtained from the current-voltage characteristics both before and after probe attachment and after hybridization with the targets. SiO 2 or gold surfaces are usually used on the floating gates. High-k dielectric materials, e.g. HfO 2 or HfSiO x , may improve the performance of the BioFETs if they can be more effectively passivated and functionalized than SiO 2 [4]. In this paper, we will report the fabrication of BioFET sensors with HfSiO x gate insulators which do not suffer from parasitic leakage effects in solution which result from the crystallization of HfO 2 . Results showing the direct electronic detection of surface functionalization, DNA attachment, and hybridization on the gate surface will be described and compared with estimates from the model.The fabrication of the BioFETs followed standard MOS fabrication processes. HfSiO x film was grown on top of 80 Ǻ thermal oxide by atomic layer deposition and MOS compatible post-processes were applied to expose the gate insulator after device fabrication. The processed chips were wire-bonded to a header and polydimethylsiloxane rings were attached to contain the phosphate-buffered saline electrolytes during the measurements.The pH sensitivity was measured before and after the HfSiO x gate was functionalized with Glycidoxypropyl trimethoxysilane (GPTMS) vapor. After functionalization, the sensitivity decreased from 31.4 mV/pH to 24.6 mV/pH due to the passivation of some of the O-H bonds on the HfSiO x surface by GPTMS. Fig. 1 shows the BioFET threshold shift due to a change in electrolyte concentration from 0.015 M to 0.3 M before DNA probes were immobilized onto the surface. The large initial negative transient is caused by a temporary change in the surface pH due to the establishment of a diffusion potential in the well. After mixing and flushing, this signal is reduced, resulting in a small net shift in the threshold voltage which was partially compensated by the initial drift of the Ag/AgCl micro-reference electrode. After the amine-modified 34 mer ssDNA probe molecules (concatenated 17 mer sequence) were attached to the surface in 0.3 M buffer, the buffer solution concentration was reduced, and then cycled from 0.015 M to 0.3 M. A significant threshold voltage change of 33 mV was observed in Fig. 2(a) as a result of the concentration change, indicating that the BioFET is very sensitive to the probe molecules. Fig. 2(b) shows the threshold voltage changes after 17 mer complementary DNA target molecules were applied; the hybridization caused a net increase in the threshold voltage shift of 3mV, which is comparable to the result from BioFETs with SiO 2 gate insulators. Noncomplementary targets produced no net shift.The model shows that a larger hybridization signal is expected when more O-H bonds are passivated by surface functionalization and / or the probe DNA molecule density ...

A BioFET array can be fabricated by post-processing of a standard CMOS chip if temperatures are kept below 450 ° and radiation or ion-bombardment damage is minimized. The processing starts with encapsulation by deposition of a low stress, electrolyte-impermeable silicon nitride layer by PECVD at 375 °C. Anisotropic reactive ion etching with an inductively coupled plasma using C4F8 and Ar was used to remove the silicon nitride and oxide layers above the poly-silicon gates. The poly-silicon was then etched off using a selective wet etch. The effect of the processing was characterized by making current-voltage and capacitance-voltage measurements with MOS capacitor structures at each stage of processing and results showed that trapped charges or interface states could be annealed out at low temperatures. Scanning electron microscopy was used to examine the cross-section of the gate areas after the etching. The results of current-voltage measurements with a Ag/AgCl reference electrode on devices in electrolyte solutions were compared to the results of charge-sheet model calculations including the effect of amphoteric charging sites on the oxide and the potential drops in the electrolyte. Measurements showing the threshold shifts subsequently produced by DNA probe attachment and hybridization will also be presented.

The unique and tunable optical properties of metal nanoparticles have attracted intense and sustained academic attention in recent years. In tandem with the demand for low-cost responsive materials, one particular topic of interest is the development of mechanically responsive device structures. This work describes the design, fabrication, and testing of a mechanically responsive plasmonic device structure that has been integrated onto a standard commercial plastic substrate. With a low actuation force and a visually perceivable color shift, this device would be attractive for applications requiring responsive features that can be activated by the human hand.

Corporate promotion of the 350 or so products and services available from the ICI/IMI Group for the Offshore Oil and Gas Industries is the task of a special unit—ICI Offshore, of London. Dr Alasdair Rankin of that organisation outlines some of the solutions to corrosion problems of offshore structures offered by this range of products.