Very deep sub-micron, entirely digital, position resolution sensors.

该项目介绍了一种由全数字电路构成的新型硅辐射探测器。这是相对于当前的、良好建立的固态传感器架构的设计方法的完全改变。这些都是非常成功的，是许多科学和技术应用的主要工具。硅传感器的一个优势是它们的位置分辨率。它们被引入和发展用于高能物理实验中跟踪带电粒子，并经过多年的不断改进。尽管如此，他们的命中位置分辨率多年来没有改善。30多年前已经实现了1微米的值，目前最好的设备具有大于几微米的分辨率。不能提高像素传感器上的命中位置精度的主要原因是放大由电离辐射释放的信号的模拟电路所需的最小尺寸，使得最小像素尺寸为几十微米的量级。这里提出的实现硅传感器的命中分辨率性能的突破的方法包括设计基于完全数字电路的传感器。感测机制是二进制的，当电离辐射穿过给定像素时，传感器单元将状态从两个可能值中的一个改变到另一个（类似于固态数字存储器的操作）。该数字电路包括有限数量的晶体管（从3到10），允许非常小的像素占用面积。根据所选CMOS技术节点的特征尺寸，单个像素可以小至100 × 100 nm2，与当前最先进的技术相比，分辨率提高了两个数量级。具有上述特征的数字辐射传感器的概念已经得到了项目支持者的验证，成功测量了脉冲蓝色激光和141 Am放射源的α粒子产生的电荷。对第一个数字传感器原型的初步测量也表明了随后的研究步骤，以提高这些设备的检测效率性能（记录的命中数与交叉电离粒子总数的比值）。结果表明，原型实现了非常浅的电荷收集，导致效率降低，仅限于在敏感晶体管栅极对应处发生的撞击，而不是在整个传感器区域上。该项目将通过敏感节点的专用设计来纠正这种低效率，并在整个电离辐射光谱（最小电离粒子，带电离子，光子）上产生非常精确的分辨率像素传感器。新的传感器将有无数的应用。在科学方面，它们将彻底改变核和粒子物理学实验，允许大幅度减少跟踪体积，在未来实验的范围和成本方面带来巨大好处。新的传感器还将能够跟踪单个硅层内小于1微米的粒子路径，从而可以定向检测反冲核或电子。这将使它们能够用于探测暗物质的难以捉摸的弱相互作用大质量粒子（WIMP）候选者。WIMP可以与硅晶格中的原子核相互作用，导致这些原子核在几百nm的距离内反冲。探测到这些短轨道并能够确定入射粒子的方向，为从其他难以克服的中微子背景中提取WIMP信号提供了一个强大的处理方法。这些只是这些新设备的巨大范围的例子。

The project introduces a novel type of silicon radiation detectors constituted by an entirely digital circuit. This is a total change of design approach with respect to the current, well established architecture of solid state sensors. These have been very successful and are the main tool for many applications in science and technology. One strength of silicon sensors is their position resolution. They have been introduced and developed for tracking charged particles in high energy physics experiment and have gone through the years to a continuous series of improvements. Nonetheless their hit position resolution has not improved for many years. A value of 1 micron was already achieved over 30 years ago, and the current best devices have resolution larger than a few microns. The main reason for the inability of improving the hit location precision on a pixel sensor is the minimum size required by the analogue circuit amplifying the signal released by the ionising radiation, making the minimum pixel dimensions of the order of a few tens of microns. The approach here proposed to realise a breakthrough for the hit resolution performance of silicon sensors consists in designing a sensor based on an entirely digital circuit. The sensing mechanism is binary, with a sensor cell changing state from one to the other of two possible values when ionising radiation is crossing a given pixel (similar to the operation of a solid state digital memory). This digital circuit is comprising a limited number of transistors (from 3 to 10), allowing for a very small pixel footprint. Depending on the feature size of the selected CMOS technology node, a single pixel could be as small as 100x100 nm2, enabling an enhancement of up to two orders of magnitude in resolution when compared to current state-of-the-art. The concept of a digital radiation sensor with the above characteristics has been validated by the proponents of the project, with successful measurements of the charge generated by a pulsed blue laser and alpha particles from a 141 Am radioactive source. The initial measurements on the very first digital sensor prototypes have also indicated the subsequent research steps to improve the detection efficiency performance (number of recorded hits over the total number of crossing ionising particles) of these devices. The results have shown that a very shallow charge collection was achieved with the prototype resulting in a reduced efficiency, limited to hits happening in correspondence of the sensitive transistor gate, rather then over the whole sensor area. This project will correct this inefficiency with dedicated design of the sensitive node and produce very precise resolution pixel sensors with high efficiency over the full ionising radiation spectrum (minimum ionising particles, charged ions, photons). The new sensors would have countless applications. In science, they would revolutionize experiments in nuclear and particle physics, allowing for a large reduction of the tracking volume, with great benefits in terms of the scope and cost of future experiments. The new sensors will also be able to track particle paths shorter than 1 micron inside a single silicon layer, allowing for directional detection of recoiling nuclei or electrons. This would enable their use for detection of elusive Weakly Interactive Massive Particle (WIMP) candidates for Dark Matter. WIMPs can interact with nuclei in the silicon lattice causing these to recoil over distances a few hundred nm. Detecting these short tracks and being able to determine the direction of the incoming particle provides a powerful handle to extract the WIMP signal from otherwise insurmountable neutrino background. These are only examples of the huge scope of these novel devices.