The Secretary of State for Defence in Her Britannic Majesty's Government

Qinetiq Limited

Anthony B Dean

Charles Thomas Elliott

Timothy Ashley

Anthony M White

Timothy Jonathan Phillips

Robin F Farrow

Piero Migliorato

Gerald M Williams

David J Wilson

Ian C Carmichael

David T Dutton

Peter N Dennis

A method of forming three-dimensional structures on a substrate by a single reactive ion each run whereby a mask is formed on said substrate before a series of iterations are carried out, each iteration including a mask etch and a substrate etch, so that successive iterations give life to reduction in the mask area and exposure of further areas of substrate.

Three dimensional etching process

A field effect transistor (FET) is of the type which employs base biasing to depress the intrinsic contribution to conduction and reduce leakage current. It incorporates four successive layers ( to ): a p InSb base layer ( ), a InAlSb barrier layer ( ), a &pgr; intrinsic layer ( ) and an insulating SiO layer ( ); p source and drain regions ( ) are implanted in the intrinsic layer ( ). The FET is an enhancement mode MISFET ( ) in which biasing establishes the FET channel in the intrinsic layer ( ). The insulating layer ( ) has a substantially flat surface supporting a gate contact ( ). This avoids or reduces departures from channel straightness caused by intrusion of a gate groove, and enables a high value of current gain cut-off frequency to be obtained. In FETs with layers that are not flat, departures from channel straightness should not be more than 50 nm in extent, preferably less than 5 nm.

High frequency field effect transistor with carrier extraction to reduce intrinsic conduction

A thermal imaging device having both serial and parallel content is provided by a number of infra-red radiation detector strips supported side by side on an insulating substrate, each strip having a number of read-out regions. To allow connection from the side of the device to the innermost detector strips, conductors err end across outer strips. These conductors may extend over the strips and over insulating material therebetween. Alternatively the conductors may be in the form of conductive tracks embodied in a substrate of semiconductor material. The strips may be indented at the read-out regions to provide, with very close spacing, sufficient room for contact between the read-out regions and the conductive tracks. Preformed aluminium contact pads may be used between bridging links to the read-out regions and the conductive tracks the contact pads and preformed tracks being centered during preformation to ensure a good ohmic contact.

Thermal imaging devices

An optically immersed infra-red detector assembly comprises a planar sapphire substrate bearing a detector with radially disposed lens contact pads. The detector and contact pads are produced by etching a single portion of cadmium mercury telluride and have mutually coplanar surfaces. A hemispherical silicon optical immersion lens is bonded to the pads by applying dilute adhesive to lens-pad interfaces. Capillary attraction draws the adhesive between the lens and the pads to form very thin layers of adhesive after solvent evaporation. The adhesive layers ensure that an air gap is produced between the lens and detector, the gap being much smaller than the infra-red wavelength of interest as required to ensure optical immersion of the detector by the lens.

Optically immersed detector assembly

A photo diode formed by a substrate of Cd.sub.x Hg.sub.1-x Te covered with a layer of CdTe forming a p-n junction. The substrate may be p-type in which case the layer is n-type or vice versa. An array of photo diodes may be formed by covering the substrate with semi-insulating CdTe and forming islets of In on the CdTe. Heating causes In to diffuse into the CdTe doping it n-type. This results in regions of n-type CdTe surrounded by semi-insulating CdTe each region forming, with the substrate, a photo diode. The heating also causes diffusion between the Cd.sub.x Hg.sub.1-x Te and CdTe to give a graded heterostructure. Electrical connections are made to the substrate, and each n-type region. The n-type CdTe region may alternatively be formed by molecular beam epitaxial growth techniques using a beam of In dopant.

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Malvern, United Kingdom

Anthony B Dean