A Novel Active Anode for Improved Photomultiplier Dynamic Range and Lifetime

Lead Research Organisation: University of Liverpool
Department Name: Centre for Materials and Structures

Abstract

Despite advances in the performance of solid state photon counting devices, microchannel plate (MCP) photomultipliers remain the technology of choice for sub-200 picosecond event timing used in applications in particle and nuclear physics, and have application in other fields including life sciences, biological microscopy, for remote sensing and surveillance, materials analysis, fusion physics and space science instrumentation.

Current MCP photomultiplier designs have performance limitations which restrict their application. These are (i) limited maximum count rate, and (ii) limited detector lifetime.

We propose to add a gain stage behind the MCP stack by coating the anode with secondary electron emitting material, and collecting the charge on a mesh between the anode readout interface and MCP. An extra gain stage providing an amplification of ~10 would lower the gain required in the MCP stack by an order of magnitude, increasing both the local and global count rate limits imposed by the MCP and would further enhance the detector lifetime beyond that achieved by MCPs. The technique can be used with both conventional multi-anodes and the Image Charge technique can easily be adapted to provide gain by converting its resistive layer to a high emission dynode and inserting a transparent conductive mesh between MCP and dynode to act as an anode.

Suitable materials for a dynode material such as SiO2, Si3N4, Al2O3, MgO and BaO would be subject to charge-up. However ALD coating can overcome this problem by layering dopant materials to control the material resistivity.

A key issue in the proposed development is the deposition of thin film coatings with a tailored combination of electrical sheet resistance (100kohm per square - 100Mohm per square) and secondary electron emission. Candidate materials include alumina, magnesia and zinc oxide in their doped and pure compositions. ALD will be used in this project to prepare films on the MCP-dynode assemblies to be developed. ALD is a batch manufacturing process capable of highly conformal, pin-hole free and large area coatings. The technique has become a core manufacturing process for the deposition of 'high-k' dielectrics in current computer processor and memory devices where atomic control of thickness and uniformity is needed.

The Space Research Centre, University of Leicester, has long record of successful collaboration with Photek Ltd. focussed on development and commercialisation of novel concepts and techniques for photon counting, imaging detector systems. Photek have existing links with Professor Chalker at Liverpool and the proposed collaboration has already manufactured, characterised and tested a preliminary batch of ALD-coated samples which has provides promising technical justification for this proposal.

This collaboration has identified a novel technique of applying ALD coatings to enhance MCP photomultiplier dynamic range and lifetime which is patentable and highly complementary to existing devices. We have made preliminary measurements of candidate ALD coatings manufactured by Liverpool, demonstrated proof-of-concept of the image charge dynode/mesh anode gain technique in an MCP detector, and made a patent application to protect our IP.
We envisage that this technique, by providing significant detector dynamic range and lifetime benefits, will give Photek considerable advantage as detector providers for new projects at sLHC and FAIR. In addition the technique is applicable to many MCP-based photomultiplier designs for which there are significant markets in other areas including in fusion physics, remote sensing, life sciences, from biological R&D to clinical diagnostics, materials analysis and planetary science.

Publications

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Description This feasibility study (Mini-IPS) was part of a joint project with the University of Leicester (Prof Jon Lapington). The project partner was Photek Ltd. Our involvement was the development of ultrathin films deposited via atomic layer deposition (ALD). The rationale for the functional coatings was to modify the surface of Photek detector elements to change their electron emission characteristics, thereby influencing the sensitivity and speed of the detectors. Properties of the emissive coatings including thickness and composition have been optimised for the detector application
Exploitation Route The company has exploited these findings in a Knowledge Transfer Partnership project led by Dr Richard Potter. The main aim of Photek's KTP with the University of Liverpool was to introduce a coating treatment capability for Microchannel Plates (MCPs), a key component in nearly all of its products. Photek found that some of its key markets, including particle physics facilities like CERN, were on the verge of dismissing its product, because of the relatively short life span of the MCPs under the operating conditions of its chambers. Improving its lifetime was one of the key aspects of improving overall device performance. Photek have now incorporated the atomic layer deposition process in house and are using it to manufacture photomultiplier tubes and channel plate detectors.
Sectors Electronics

 
Description The project has developed secondary electron emission coatings, which have been exploited in detector systems. The industrial collaborator Photek is now engaged with Liverpool to exploit the project outcomes via a Knowledge Transfer Partnership which is now completed. The company has taken the atomic layer deposition in-house and is using processes developed under the STFC and KTP projects in its detector product range.
First Year Of Impact 2017
Sector Electronics
Impact Types Economic

 
Description Knowledge Transfer Partnership
Amount £196,576 (GBP)
Funding ID KTP009766 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 08/2014 
End 04/2019
 
Description A Novel Active Anode for Improved Photomultiplier Dynamic Range and Lifetime 
Organisation Photek Ltd.
Department Research and Development
Country United Kingdom 
Sector Private 
PI Contribution This collaboration is exploring the use of ultrathin oxide layers in photomultipliers Photek are now working with Liverpool to exploit the project outcomes via a Knowledge Transfer Partnership project.
Collaborator Contribution The University of Leicester is measuring the secondary electron emission characteristics of the thin films deposited at Liverpool. Photek Ltd is exploring the use of these materials in a photomultiplier tube.
Impact None to date
Start Year 2013
 
Description A Novel Active Anode for Improved Photomultiplier Dynamic Range and Lifetime 
Organisation University of Leicester
Department Department of Physics & Astronomy
Country United Kingdom 
Sector Academic/University 
PI Contribution This collaboration is exploring the use of ultrathin oxide layers in photomultipliers Photek are now working with Liverpool to exploit the project outcomes via a Knowledge Transfer Partnership project.
Collaborator Contribution The University of Leicester is measuring the secondary electron emission characteristics of the thin films deposited at Liverpool. Photek Ltd is exploring the use of these materials in a photomultiplier tube.
Impact None to date
Start Year 2013