PPubMed15 Mar 2012Cited 22×

Micrometre resolution of a charge integrating microstrip detector with single photon sensitivity Charge integrating microstrip detector

A. Schubert, A. Bergamaschi, C. David, R. Dinapoli, S. Elbracht-Leong, S. Gorelick, H. Graafsma, B. Henrich, I. Johnson, M. Lohmann, A. Mozzanica, V. Radicci, R. Rassool, L. Schädler, B. Schmitt, X. Shi, B. Sobott

Abstract

The spatial resolution of a single-photon-resolving integrating system has been improved using a non-linear charge interpolation approach. The resolution limit for a 20 µm-pitch sensor is presented.

A figure from Micrometre resolution of a charge integrating microstrip detector with single photon sensitivity Charge integrating microstrip detector — fig. from the paper

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Non‑linear charge interpolation on a GOTTHARD microstrip detector achieves sub‑2 µm spatial resolution for 20 µm‑pitch sensors.

What’s new

i.Implemented a non‑linear η‑algorithm for charge interpolation in a charge‑integrating microstrip detector
ii.Demonstrated experimental spatial resolution of ~1.8 µm and simulated lower limit of ~0.8 µm for a 20 µm‑pitch sensor
iii.Validated the approach with detailed Geant4/TCAD simulations linking sensor geometry, noise and coupling to resolution
iv.Imaged sub‑2 µm structures, including 10 µm gold lines and 7 µm letters, showing practical high‑resolution capability
v.Identified detector noise and alignment as key factors limiting further resolution improvement

How they did it

The GOTTHARD chip (100 channels, 0.25 µm CMOS) was bonded to a 20 µm‑pitch silicon strip sensor and read out via a FPGA‑controlled DAQ with 14‑bit 80 MHz ADCs. A non‑linear η‑algorithm was applied to the analog charge signals after flat‑field calibration for each strip pair. Spatial resolution was measured by scanning a 2 µm tungsten slit across the sensor in 1 µm steps and comparing motor positions to reconstructed hit positions, complemented by Geant4‑based charge generation and TCAD charge transport simulations.

What they found

Experimental PSF σₓ ≈ 1.8 ± 0.1 µm (conservative estimate)
Simulated lower‑limit σₓ ≈ 0.8 µm for 20 µm pitch
Reconstruction error σₓ = 1.38 ± 0.04 µm at strip centre and 0.40 ± 0.03 µm near strip boundary
Measured ENC 334 ± 8 e⁻ (25 µm) and 370 ± 19 e⁻ (20 µm)
Coupling factor K ≈ 0.05–0.07 (≈7 % measured)
Contrast of 10 µm Au lines 52 ± 8 % with measured line width 10.4 ± 0.9 µm

Caveats

✕Resolution limited by slit‑to‑strip alignment (≈1° uncertainty causing ~1.7 µm error)
✕Simulation underestimates strip coupling because preamp charge‑integration effects are not fully modeled
✕Noise variation across strips leads to ~10 % spatial‑resolution variation
✕Achieving sub‑micrometre resolution requires noise reduction to ~100 e⁻, which is not yet realized

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