A second monolithic silicon pixel prototype was produced for
the MONOLITH project. The ASIC contains a matrix of hexagonal pixels
with 100 μm pitch, readout by a low-noise and very fast SiGe HBT
frontend electronics. Wafers with 50 μm thick epilayer of
350 Ωcm resistivity were used to produce a fully depleted
sensor. Laboratory and testbeam measurements of the analog channels
present in the pixel matrix show that the sensor has a 130 V wide
bias-voltage operation plateau at which the efficiency is 99.8%.
Although this prototype does not include an internal gain layer, the
design optimised for timing of the sensor and the front-end
electronics provides a time resolutions of 20 ps.
Major advances in silicon pixel detectors, with outstanding timing performance, have recently attracted significant attention in the community. In this work we present and discuss the use of state-of-the-art Geiger-mode APDs, also known as single-photon avalanche diodes (SPADs), for the detection of minimum ionizing particles (MIPs) with best-in-class timing resolution. The SPADs were implemented in standard CMOS technology and integrated with on-chip quenching and recharge circuitry. Two devices in coincidence allowed to measure the time-of-flight of 180 GeV/c momentum pions with a coincidence time resolution of 22 ps FWHM (9.4 ps Gaussian sigma). Radiation hardness measurements, also presented here, highlight the suitability of this family of devices for a wide range of high energy physics (HEP) applications.
The Picosecond Avalanche Detector is a multi-junction
silicon pixel detector based on a (NP)drift(NP)gain
structure, devised to enable charged-particle tracking with high
spatial resolution and picosecond time-stamp capability. It uses a
continuous junction deep inside the sensor volume to amplify the
primary charge produced by ionizing radiation in a thin absorption
layer. The signal is then induced by the secondary charges moving
inside a thicker drift region. A proof-of-concept monolithic
prototype, consisting of a matrix of hexagonal pixels with
100 μm pitch, has been produced using the 130 nm SiGe BiCMOS
process by IHP microelectronics. Measurements on probe station and
with a 55Fe X-ray source show that the prototype is functional
and displays avalanche gain up to a maximum electron gain of 23. A
study of the avalanche characteristics, corroborated by TCAD
simulations, indicates that space-charge effects due to the large
primary charge produced by the conversion of X-rays from the
^55Fe source limits the effective gain.
The proof-of-concept prototype of the Picosecond Avalanche
Detector, a multi-PN junction monolithic silicon detector with
continuous gain layer deep in the sensor depleted region, was tested
with a beam of 180 GeV pions at the CERN SPS. The prototype
features low noise and fast SiGe BiCMOS frontend electronics and
hexagonal pixels with 100 μm pitch. At a sensor bias voltage
of 125 V, the detector provides full efficiency and average time
resolution of 30, 25 and 17 ps in the overall pixel area for a
power consumption of 0.4, 0.9 and 2.7 W/cm2, respectively. In
this first prototype the time resolution depends significantly on
the distance from the center of the pixel, varying at the highest
power consumption measured between 13 ps at the center of the pixel
and 25 ps in the inter-pixel region.
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