A Novel Active Anode for Improved Photomultiplier Dynamic Range and Lifetime

尽管固态光子计数器件的性能有所进步，但微通道板（MCP）光电倍增管仍然是粒子和核物理应用中用于200皮秒以下事件定时的首选技术，并在其他领域有应用，包括生命科学，生物显微镜，遥感和监测，材料分析，聚变物理和空间科学仪器。目前的MCP光电倍增管设计存在性能限制，限制了其应用。它们是(i)有限的最大计数率和（ii）有限的检测器寿命。我们建议在阳极表面涂覆二次电子发射材料，并在阳极读出接口和MCP之间的网格上收集电荷，从而在MCP堆栈后面增加一个增益级。提供~10放大的额外增益级将使MCP堆栈所需的增益降低一个数量级，增加MCP施加的本地和全局计数率限制，并将进一步提高检测器的寿命，超过MCP所达到的寿命。该技术既可以用于传统的多阳极，也可以通过将其电阻层转换为高发射dynode，并在MCP和dynode之间插入透明导电网格作为阳极，轻松地适应图像电荷技术以提供增益。合适的材料如SiO2， Si3N4, Al2O3， MgO和BaO将会被充电。然而，ALD涂层可以通过分层掺杂材料来控制材料的电阻率来克服这一问题。提出的发展的一个关键问题是薄膜涂层的沉积，具有定制的电阻（每平方100欧姆-每平方100欧姆）和二次电子发射的组合。候选材料包括掺杂和纯成分的氧化铝、氧化镁和氧化锌。ALD将在该项目中用于制备待开发的MCP-dynode组件上的薄膜。ALD是一种批量制造工艺，能够生产高度适形，无针孔和大面积涂层。该技术已成为当前计算机处理器和存储设备中沉积“高k”介电体的核心制造工艺，这些设备需要对厚度和均匀性进行原子控制。莱斯特大学空间研究中心与Photek有限公司在光子计数、成像探测器系统的新概念和技术的开发和商业化方面有着长期的成功合作记录。Photek与利物浦的Chalker教授有联系，提议的合作已经制造，表征和测试了一批初步的ald涂层样品，这为该提议提供了有希望的技术理由。此次合作确定了一种应用ALD涂层来提高MCP光电倍增管动态范围和寿命的新技术，该技术可申请专利，并与现有设备高度互补。我们已经对利物浦生产的候选ALD涂层进行了初步测量，在MCP探测器中演示了图像电荷dynode/网状阳极增益技术的概念验证，并申请了专利以保护我们的知识产权。我们设想这种技术，通过提供显著的探测器动态范围和寿命优势，将使Photek作为sLHC和FAIR新项目的探测器供应商具有相当大的优势。此外，该技术还适用于许多基于mcp的光电倍增管设计，这些光电倍增管在聚变物理、遥感、生命科学、从生物研发到临床诊断、材料分析和行星科学等其他领域都有重要的市场。

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.