This time we will explain our product SDD (Silicon drift detector), which is often used in X-ray spectrometers.

The typical Silicon Drift Detector (SDD) is a type of Energy Dispersive X-ray Detector (EDX) and is a semiconductor detector.

Compared to conventional silicon semiconductor detectors (Si(Li) detectors), it allows for high- count processing with the same energy resolution.
Additionally, because it operates with cooling via a Peltier element, there is no need for liquid nitrogen cooling, which makes the entire detector compact and lightweight.

The SDD is made of high-purity silicon and has ring-shaped electrodes. The drift electric field generated by these electrodes moves the charge generated by X-rays, which is then collected by a small collection electrode. The amount of charge collected is proportional to the incident X-ray energy, allowing for energy measurement of the X-rays.

The SDD features concentric electrodes with a central collection electrode. This electrode connects to an external FET, which converts and amplifies the charge into a voltage.

Placing the FET at the center of the ring electrode reduces electrical noise and enhances energy resolution by minimizing capacitance between the collecting electrode and the FET.

Models with ASIC specifications offer even better resolution. SDDs are utilized in scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray fluorescence (XRF and TXRF), and X-ray absorption fine structure analysis (XAFS).

TechnoAP’ s SDD system is extensively used in XAFS studies at synchrotron radiation facilities.

The detector is housed in a cylindrical casing and connects easily to a vacuum chamber via flanges. Available in single and multi-element (4/7) configurations, the SDD offers options for detection windows in graphene or WL (windowless) types. The multi-element version provides higher sensitivity and count rates.

Fig.1 Single element SDD detector

Fig.2 7-element SDD detector

Fig.3 shows the case where the detection window is graphene and the case where the beryllium window is used. Beryllium windows were the mainstream until recently, but graphene windows offer superior detection sensitivity in the low energy region.

Fig.3 Comparison of beryllium window and graphene window

• CH type (for high energy)
• 1μm thick carbon
• No support grid
• Comparison of beryllium window and graphene window 1μm

The energy resolution of the SDD is defined for the characteristic X-ray Mn Kα peak at 5.9 keV, corresponding to approximately 125-130 eV.

Fig. 4 shows the spectrum of the X-ray source Fe-55. The resolution in Fig. 4 is 125 eV, representing the highest performance. There is some variation in the SDDs we receive, with the average being about 128 eV, so 125 eV is an excellent result.

Fig.4 Spectrum at Fe-55

Our SDD offers excellent resolution with a rise time of just 1 μs. The flattop is set to the preamp's maximum rise time of 350 ns.

While high-count measurements are possible with a shorter rise time, for XAFS measurements, where high counts are crucial, the rise time can be reduced to below 300 ns.

Fig.5 1μs trapezoidal shaping

Fig.6 Spectrum risetime 1000ns flattop 350ns on Fe-55 with 4-element SDD


Fig.7 4-element SDD(With vertical movement mechanism)

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References
[1] Gordon,Gilmore, Practical Gamma-Ray Spectrometry,( Johnwiley&Sons Ltd, 1995）
[2] Glenn F.Knoll, Radiation Detection and Measurement 4th Edition, (Ohmsha, 2013)