This is your life

Sometimes history produces a conjunction of factors that foster an unprecedented burst of technical innovation in one location. It’s a phenomenon famously identified in the growth of Silicon Valley. But it’s not just a US phenomenon: a similar effect occurred much closer to home during the mid to late 20th century –Plessey’s Allen Clark Research Centre at Caswell, now owned by Bookham Technology. It is recognised that both the GaAs mesfet and the GaAs monolithic ic were invented and developed at Caswell, but what is probably less well known is that scientists on the site were working on silicon ic technology almost 18 months before Jack Kilby demonstrated the first working ic at Texas Instruments in Dallas. Caswell technologists also developed the first multilayer ceramic capacitor and a host of other inventions that enabled many of the electronic products we rely on today – including mobile phones, satellite tv, WiFi and RFID. Many influential names in today’s electronics industry began their careers at Caswell and a huge number of successful companies owe their technical and commercial success either directly or indirectly to Caswell developed technology. Despite its reputation for semiconductor research, it was passive devices that were the main focus when Plessey first moved its research laboratories to Caswell in October 1940, in order to escape enemy bombing around London. At the time, the site comprised a country house with a working farm, situated four miles from the small market town of Towcester. Pigs and geese continued to be a feature of the environment until the mid 1950s, when the labs outgrew the farm buildings and the first purpose built structure was added. The laboratories were run by Geoffrey Gaut, an ambitious and forward thinking scientist who had joined Plessey as a new graduate in 1934. Projects under way at the time of the move included: the miniaturisation of electrolytic capacitors; cobalt ferrites for magnetic recording tape; high power variable resistors; and semiconducting ceramics and high temperature ceramic/metal composites (cermets). An early breakthrough was the invention in 1948 of Radar Absorbent Material (RAM). This technology, later dubbed ‘Stealth’ by the US, went on to provide a crucial tactical advantage to British naval and airborne forces in the Falklands and both Gulf Wars. It is still being developed and manufactured in Towcester as part of BAE Systems. Work on solid state silicon crystal growth and purification began at Caswell in 1952 and this formed the basis both for rectifier production in Towcester and for development programmes during the 1950s and early 1960s in radiation detectors, photocells and solar cells. Even the term ‘solid state’ was invented at Caswell, to distinguish semiconductor devices from their valve predecessors. Kilby himself acknowledged that it was Geoffrey Dummer of the Government’s Telecommunications Research Establishment (TRE, later RSRE) at Malvern who first suggested the idea of the ic in 1952, as a result of discussions at Plessey Caswell with Gaut. In April 1957, TRE granted Caswell a research programme towards realising a silicon ic and a wooden space model was fabricated there by John Herbert to demonstrate the concept. Considerable work had already been completed on integrating resistors and inductors by the time one of the key engineers, J T Kendall, left Caswell to work for TI. It was only months later that TI announced the realisation of the world’s first ic. Silicon ic development began in earnest at Caswell in 1958 and continued until 1991. The focus was mainly on analogue circuits, particularly amplifiers. By early 1963, it had achieved a six transistor feedback amplifier chip operating over dc to 5MHz. Many world class linear devices developed at Caswell were transferred into production at the Plessey Semiconductors plant at Cheney Manor in Swindon, which had opened in the mid 1950s to manufacture transistors. If silicon dominated Caswell’s research projects during the 1960s, then compound semiconductors, particularly GaAs, became the flagship technology of the 1970s and 1980s, spawning a manufacturing unit in Towcester. Scientists at Caswell developed the first reliable technique for producing GaAs in thin films – the arsenic trichloride vapour phase epitaxy (VPE) process – and this enabled it to achieve world leadership in Gunn diodes in the late 1960s.