Specifications and pre-production of n⁺-in-p large-format strip sensors fabricated in 6-inch silicon wafers, ATLAS18, for the Inner Tracker of the ATLAS Detector for High-Luminosity Large Hadron Collider

Abstract

The ATLAS experiment is constructing new all-silicon inner tracking system for HL-LHC. The strip detectors cover the radial extent of 40 to 100 cm. A new approach is adopted to use p-type silicon material, making the readout in n+-strips, so-called n+-in-p sensors. This allows for enhanced radiation tolerance against an order of magnitude higher particle fluence compared to the LHC. To cope with varying hit rates and occupancies as a function of radial distance, there are two barrel sensor types, the short strips (SS) for the inner 2 and the long strips (LS) for the outer 2 barrel cylinders, respectively. The barrel sensors exhibit a square, 9.8 × 9.8 cm2, geometry, the largest possible sensor area from a 6-inch wafer. The strips are laid out in parallel with a strip pitch of 75.5 μm and 4 or 2 rows of strip segments. The strips are AC-coupled and biased via polysilicon resistors. The endcap sensors employ a “stereo-annulus” geometry exhibiting a skewed-trapezoid shapes with circular edges. They are designed in 6 unique shapes, R0 to R5, corresponding to progressively increasing radial extents and which allows them to fit within the petal geometry and the 6-inch wafer maximally. The strips are in fan-out geometry with an in-built rotation angle, with a mean pitch of approximately 75 μm and 4 or 2 rows of strip segments. The eight sensor types are labeled as ATLAS18xx where xx stands for SS, LS, and R0 to R5. According to the mechanical and electrical specifications, CAD files for wafer processing were laid out, following the successful designs of prototype barrel and endcap sensors, together with a number of optimizations. A pre-production was carried out prior to the full production of the wafers. The quality of the sensors is reviewed and judged excellent through the test results carried out by vendor. These sensors are used for establishing acceptance procedures and to evaluate their performance in the ATLAS collaboration, and subsequently for pre-production of strip modules and stave and petal structures.

Establishing the Quality Assurance programme for the strip sensor production of the ATLAS tracker upgrade including irradiation with neutrons, photons and protons to HL-LHC fluences

“…The strip detectors of the outer region of the ITk, at radii (r) 40<r<100 cm, consist of 4 layers of cylinders (two Short Strip and two Long Strip) and 6 layers of disks with 6 rings of detectors (R0 to R5) in each disk. The ATLAS18 wafer design is laid out and fabricated as the pre-production and production design for the strip sensors for the ITk project [7], as shown in figure 1(a). Large area strip sensors are fabricated in substrate wafers with a diameter of 6 inches in p-type silicon, according to the design rules of HPK.…”

Setups for eliminating static charge of the ATLAS18 strip sensors

“…The ITk strip detector will expand the silicon area from 60 m 2 to 165 m 2 , while substantially improving radiation hardness and signal processing speed. The production of a total of 21 000 ITk strip sensors, including spares to the 18 000 sensors to be used in the experiment, comprising 2 types of barrel and 6 types of endcap sensors [2], has started in Hamamatsu Photonics K.K in 2021 and is scheduled for completion in 2025.…”

Monitoring Quality of ATLAS ITk Strip Sensors Through Database

“…It was preceded by a pre-production phase of 1,041 wafers in 2020. This phase included all 8 sensor types designed for production [4]. It was used as a system exercise for verification of designs, testing methodology and throughput by ATLAS sites, as well as the ability of the sites to reliably characterize the sensor performance.…”

“…It is a flexible online DB implemented as a cloud-based appli-1The design for hermeticity has two exceptions: there are gaps between the adjacent sensors in any given layer, and the sensor edge regions are inactive. The gaps are minimized and the sensor layouts use "slim edge" design [4] in order to maximize the active area fraction in each layer.…”