Development of wave form measurement method for high acuracy of detection time in semiconductor X-ray detector

半导体材料中的杂质原子以及杂质原子在纳米尺度上向晶界的偏析等微量元素对材料和器件的性能有很大的影响。为此，我们在1995年研制了一种新的分析透射电子显微镜，称为符合电子显微镜，它通过测量特征X射线和相关能量损失电子之间的符合测量来实现元素映射。在以前的符合电子显微镜系统中，一个硅(Li)探测器和一个多阳极位置灵敏光电倍增管连接在一个电子显微镜上。使用这些探测器，我们成功地缩短了测量时间，在产生特征X射线后只选择了指定的能量损失电子。先进的符合电子显微镜能够在较小的测量范围内获得元素图谱图像，但由于X射线探测范围较差，符合测量仍需要不少于几个小时的时间更准确的硅(锂)探测器。使符合门时间t最小化是进一步缩短测量时间的有效解决方案之一。符合门时间t是确定是否同时探测到X射线和敌方损失电子的有限时间窗。在我们以前的工作中，由于使用了模拟符合探测系统，Si(Li)探测器的X射线探测时间精度仍然很差，限制在100纳秒。尽管高速模拟电路的性能令人满意。第一年，我们研制了一套离线式波形测量系统，每10纳秒记录一次X射线信号的波形，使探测时间的精度达到85纳秒。第二年，我们研制了直流抑制型前置放大器，将信号的噪声降到0.3 mV，然后用现场可编程门阵列开发了100 MHz的采样系统和符合选择电路。使用这些系统，检测时间的精度降低到75纳秒。这种不准确度的极限不是由于检测信号上升时间的波动，而是由于探测器的噪声。我们认为使用低噪声和像SDD(硅漂移探测器)这样的高速探测器读数越高，时间精度越低

The characteristics of materials and devices are considerably affected by trace elements such as impurity atoms localozed in semiconductor materials and the segregation of impurity atoms to the grain boundary on the nanometer scale. For this purpose, We developed a new analytical transmission electron microscope(TEM), called the coincidence TEM in 1995, which enabled elemental mapping by the coincidence measurement between the characteristic X-ray rand relevant energy-loss electrons. In the previous coincidence TEM system, a Si(Li) detector and a multi-anode position-sensitive phtomultiplier were attached to a TEM. Using these detectors, we succeeded in shorterning measurement time by selecting only specified energy-loss electrons after generating characteristic X-rays. The advanced coincidence TEM enabled to obtain an elemental mapping image in a shrter measurement rime, but no less than several hours was still needed for the coincidence measurement due to poor X-ray detection rime ac … More curacy of a Si(Li) detector. Minimizing the coincidence gate time delta t, which is a finite time window to determine whether X-rays and enemy-loss electrons are coincidentally detected, is one of the effective solutions to further reduce measurement time. in our previous works, the X ray detection time accuracy of a Si(Li) detector was still poor due to the use of an analog coincidence detection system and limits delta.-t to 100 nano second, although the performance of the high speed analog electronic circuit was satisfactoryIn the first year, we developed a off line type wave form measurement system which record the wave form of X-ray signal in every 10 nano second, and it result the accuracy of the detection time to 85 nano second. In the second year, we developed a DC rejection type pre-amplifier which reduce the noise level of the signal to 0.3mV Then we developed a 100MHz sampling system and coincidence selecting circuit with FPGA. Using these system, the accuracy of the detection time is reduced to 75 nano second. The limit of this inaccuracy is not due to the fluctuation of the rise time of the detection signal, but due to the noize of the detector. We suppose that the use of the low noise and the high speed detector like SDD (Silicon Drift Detector) reading more higher time accuracy Less