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使用的亚200皮秒事件计时的首选技术，并且在其他领域中也有应用，包括生命科学、生物显微镜、遥感和监视、材料分析、聚变物理和空间科学仪器。目前MCP光电倍增管的设计有性能限制，限制了它们的应用。这些是（i）有限的最大计数率，和（ii）有限的探测器寿命。我们建议通过在阳极上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，在MCP堆栈后面添加一个增益级。提供~10的放大率的额外增益级将使MCP堆叠中所需的增益降低一个数量级，从而增加由MCP施加的局部和全局计数率限制，并且将进一步增强探测器寿命，超过由MCP实现的寿命。该技术可以与传统的多阳极一起使用，并且图像电荷技术可以容易地适于通过将其电阻层转换为高发射倍增电极并在MCP和倍增电极之间插入透明导电网以用作阳极来提供增益。诸如SiO2、Si 3 N4、Al 2 O3、MgO和BaO的用于倍增电极材料的合适材料将经受充电。然而ALD涂层可以通过分层掺杂材料来控制材料的结晶性来克服这个问题。在所提出的发展中的一个关键问题是沉积具有定制的薄层电阻（100 kohm/square -100 Mohm/square）和二次电子发射的组合的薄膜涂层。候选材料包括氧化铝、氧化镁和氧化锌的掺杂和纯成分。ALD将用于本项目中，以制备膜的MCP-倍增电极组件进行开发。ALD是一种能够进行高度保形、无针孔和大面积涂层的批量制造工艺。该技术已经成为当前计算机处理器和存储器设备中的“高k”电介质沉积的核心制造工艺，其中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 Ltd.有着长期的成功合作记录，专注于光子计数、成像探测器系统的新概念和技术的开发和商业化。Photek已经与利物浦的Chalker教授建立了联系，并且已经制造、表征和测试了一批初步的ALD涂层样品，这为这项提议提供了有希望的技术依据。这项合作已经确定了一种应用ALD涂层以提高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，并与现有器件高度互补。我们已经对利物浦制造的候选ALD涂层进行了初步测量，展示了MCP探测器中图像电荷倍增器/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IP。我们预计，这种技术通过提供显着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，该技术适用于许多基于MCP的光电倍增管设计，这些设计在其他领域具有重要的市场，包括聚变物理，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。

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.