Elsevier

Diamond and Related Materials

Volume 10, Issues 9–10, September–October 2001, Pages 1765-1769
Diamond and Related Materials

Broadband electronics for CVD-diamond detectors

https://doi.org/10.1016/S0925-9635(01)00434-4Get rights and content

Abstract

The application of CVD-diamond detectors for particle detection has created a demand for the development of very fast, low-noise electronics operated at high dc bias voltages. To take advantage of the high charge-carrier mobility of the new detector material the signal processing is performed using microwave layout techniques as well as picosecond pulse shapers and GHz-frequency dividers. The particle detection limits of CVD-diamond detectors processed with low impedance broadband electronics are described. The properties of the developed electronics are discussed in conjunction with results from beam diagnostics operation in the broad energy range of 120 keV/amu up to 2 GeV/amu for GSIs heavy ion accelerators.

Introduction

Polycrystalline CVD-diamond films of 10–1000 μm thickness have been commercially available for several years. After metallization of their surface, they can be used for particle detection. Charged particles passing through the CVD-diamond material generate electron–hole (e–h) pairs by their energy loss. An energy loss of 13 eV is required for each generated e–h pair. Accelerated heavy ions passing a diamond detector undergo a relatively high energy loss; it is proportional to the square of the atomic charge number Z. Thus, this detector material is well suited for applications at heavy ion accelerator facilities [1], [2]. In a CVD-diamond detector strip with an electrical capacity of 10 pF, approximately 104 e–h pairs produce a signal amplitude of 100 μV and a pulse width of 1 ns. These detectors have to be DC biased at several hundred volts.

The most remarkable features of CVD-diamond detectors are:

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    very good timing capability, due to the short rise-time (<100 ps) of the signals;

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    high counting rate capability, up to 108 to 109 particles/s due to the short output pulses;

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    zero idle counting rate due to the band gap of 5.6 eV;

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    radiation hardness, almost no structural damage at high particle fluxes; and

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    robust and simple device with respect to mechanical and electrical layout.

Section snippets

Broadband preamplifiers

Charged particles passing through the diamond detector produce short electrical pulses. The pulse rise-time of less than 100 ps is short due to the high mobility of both electrons and holes in the diamond. The pulse fall-time is determined by the electrical (RC) time constant being determined by the capacity C of the diamond electrodes and the system impedance R of the connected preamplifier. At an electrode capacity of 10 pF and a system impedance of 50 Ω, the time constant is 500 ps and the

Pulse shaping and pulse frequency dividers

The AC-coupling in the amplifier chain results in a DC baseline shift when the particle counting rate increases. Fast analog differential voltage comparators, which compare the incident input signal with a time delayed replica of itself and respond within some hundred picoseconds, perform very well as so-called leading edge discriminators, and are used at the same time to suppress the DC-baseline effect. They also provide a time-shaped digital output for the signal processing stages. The type

Pulse counting and data acquisition

A new dedicated pulse counter board has been developed. Each board contains eight counter channels with 150-MHz maximum counting frequency per channel. A counter channel is 32 bits wide and provides on-the-fly readout in time intervals. Each time interval can be defined from 10 μs to seconds with microsecond resolution. The total number of time intervals per measurement is not restricted, but the available total memory space of 4 Mbyte per board must not be exceeded. In this way, a time

Outlook

The first series of amplifiers (DBA-II) is in use for a lot of applications that were not entirely foreseen during its development 3 years ago. The use of diamond detectors for ion beams was extended to low energies around 1 MeV/amu, where the ions are stopped inside the diamond layer (used in a 120-keV/amu–1.4-MeV/amu bunch shape monitor [4]). At CERN the preamplifiers are tested together with CdTe detectors which are developed for minimum ionizing particles (MIPs), see [5]. Recently, the same

References (6)

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