Electron multiplier supply and signal processing: working towards a system on chip solution

Despite the primitive operation and challenging practicalities of electron multipliers, they still outperform solid state equivalents in professional level equipment that requires single electron or photon resolution. The advent of the Micro Electronic and Mechanical (MEMs) fabrication process has the potential to miniaturise electron multipliers to allow mass production, reduce physical volume, and minimise part to part variation. The potential impact of MEMs is greatly reduced if secondary electronics associated with such devices cannot be reduced by a similar magnitude.

The primary purpose of this research project was to develop the secondary electronics (power supply, divider and decoupling) to enable electron multiplier-based detectors to rival solid-state counterparts in terms of size and power consumption for use in a device the size of a mobile phone. To be comparable with solid state alternatives a System in Package (SiP) specification was targeted, with all specialised circuitry occupying the same package as the detector.

To realise the reduction in size required, a number of practical limitations were identified and addressed, including standard capacitor values, behaviour under DC bias and dark discharge across PCBs. These were characterized through hardware measurement, fed into theoretical models and finally electronic assemblies were then designed around these. This bottom-up methodology was shown to have performance advantages when optimising proven topologies under restrictive design limitations.

To demonstrate the size and power reduction available to new detectors, two existing topologies were optimized and evaluated using this bottom-up method. A third new topology was synthesised to better overcome identified shortcomings at a conceptual level. Performance of all three designs is reported.

This proof of concept project was based around a scintillation detector employing a photo multiplier tube. However, it is equally applicable to any discrete dynode or microchannel plate electron multiplier, such as high gain pixilated imaging systems. Devices were tested in a spectroscopic scintillation radiation detection system to valuate performance deficiencies introduced by reduction of both size and power consumption.

As MEMS manufactured devices are still in an early stage of development, this work did not attempt to demonstrate any overall comparison against solid state equivalents’ performance but demonstrated that the secondary electronics would not be the limiting factor in terms of cost or performance in the application to MEMs manufactured electron multipliers.

The project delivered three prototypes that performed against the specification, with limitations highlighted, and a brief for a SoC solution was constructed.