Speaker
Description
We focus on particle detectors for electron microscopy and especially on the image quality improvement with very high sensitivity and low-noise electron imaging. Solid-state detectors offer the advantages of direct detection, response linearity, thin and customizable geometry including arbitrary segmentation. This, in combination with signal electron filtering in the SEM objective, promises the required flexibility in contrast formation. The present work aims to achieve the ultimate performance of this type of detector, which is significantly limited by the large parasitic capacitances in today's designs, by placing the bare active silicon op-amp chip on the sensor substrate.
We present the design and measured performance of an ASIC-like transimpedance amplifier based on bare-die op-amps placed directly on the sensor substrate. This leads to a reduction in input capacitance, fine controlling of stray parameters and ultra-low-noise performance. It is a cost-effective solution tailored for pixel imaging, strip or segmented detectors with a few pF input capacitance. A hybrid integrated circuit PoP with a two TIA channels was designed and wire-bonded to the detector segment. We have successfully used this approach to construct a high-sensitivity, high-bandwidth BSE detector capable of 25 ns dwell time, which is an order of magnitude better than currently used solutions. We are investigating the effects of PCB leakage, excess noise from resistors, parasitic capacitance that limits bandwidth, local overheating of electronics in vacuum, and ways of using ceramic substrates instead of conventional laminate substrates. The result is a new and more sophisticated front-end circuit to extract the signals, as in the case of hybrid pixel technology.
