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Ring oscillator performance of the ATLAS inner tracker pixel readout chip

Yahya Khwaira, Abdenour Lounis, Maurice Cohen-Solal, Mohsine Menouni, Pierre Barrillon, Denis Fougeron

TL;DR

The paper characterizes Ring Oscillators fabricated in 65-nm CMOS for the ATLAS ITk pixel readout, focusing on how temperature, supply voltage, total ionizing dose, and annealing influence RO frequency and propagation delay. It combines Cadence-based simulations with an extensive irradiation campaign (up to 520 Mrad) and high-temperature annealing to validate and interpret RO behavior in ITkPixV1.1, including drive-strength variants Str-0 and Str-4 and multiple gate types. Key findings show temperature depresses RO frequency via mobility reduction, TID induces threshold shifts that increase $T_{pd}$, and that Str-0 is more radiation-sensitive while Str-4 is more radiation-tolerant; annealing partially restores performance. The work provides actionable guidance for radiator-hard RO design and biasing strategies in HL-LHC ITk readout designs, supported by simulation-validated trends and dose-dependent recovery observations.

Abstract

This paper presents experimental and simulation data to characterize the Ring Oscillators (RO) produced in 65-nm CMOS technology for the next promising generation of readout chips for the pixel detector in the Inner Tracker (ITk) at the ATLAS experiment at CERN. To enable a better understanding of the RO block embedded in ITkPixV1.1 single chip card (SCC), tests at various temperatures, voltages, accumulated total ionizing dose (TID) with X-ray irradiation, and high-temperature annealing will be presented. The objective of this study is to examine the RO output dependency based on different variable conditions and provide simulation data using Cadence, an electronic design automation (EDA) software to validate the experimental outcomes.

Ring oscillator performance of the ATLAS inner tracker pixel readout chip

TL;DR

The paper characterizes Ring Oscillators fabricated in 65-nm CMOS for the ATLAS ITk pixel readout, focusing on how temperature, supply voltage, total ionizing dose, and annealing influence RO frequency and propagation delay. It combines Cadence-based simulations with an extensive irradiation campaign (up to 520 Mrad) and high-temperature annealing to validate and interpret RO behavior in ITkPixV1.1, including drive-strength variants Str-0 and Str-4 and multiple gate types. Key findings show temperature depresses RO frequency via mobility reduction, TID induces threshold shifts that increase , and that Str-0 is more radiation-sensitive while Str-4 is more radiation-tolerant; annealing partially restores performance. The work provides actionable guidance for radiator-hard RO design and biasing strategies in HL-LHC ITk readout designs, supported by simulation-validated trends and dose-dependent recovery observations.

Abstract

This paper presents experimental and simulation data to characterize the Ring Oscillators (RO) produced in 65-nm CMOS technology for the next promising generation of readout chips for the pixel detector in the Inner Tracker (ITk) at the ATLAS experiment at CERN. To enable a better understanding of the RO block embedded in ITkPixV1.1 single chip card (SCC), tests at various temperatures, voltages, accumulated total ionizing dose (TID) with X-ray irradiation, and high-temperature annealing will be presented. The objective of this study is to examine the RO output dependency based on different variable conditions and provide simulation data using Cadence, an electronic design automation (EDA) software to validate the experimental outcomes.
Paper Structure (11 sections, 6 equations, 7 figures)

This paper contains 11 sections, 6 equations, 7 figures.

Table of Contents

  1. Introduction
  2. The Ring oscillator device
  3. Temperature effects
  4. TID effects
  5. Ring Oscillator in ITkPixV1.1
  6. Cadence Simulation
  7. Experimental Validation
  8. Temperature Tests
  9. Supply Voltage Tests
  10. Irradiation Setup and Results
  11. Conclusion

Figures (7)

  • Figure 1: Basic RO circuit with N number of gates.
  • Figure 2: Fundamental radiation-induced electron-hole pair generation with bulk hole and interface trapping.
  • Figure 3: Experimental setup with SCC inside a climate chamber.
  • Figure 4: Comparison of RO frequency oscillation as a function of supply voltage and temperature. Experimental measurements (markers) are compared with simulation results (dashed lines). The voltage dependence is shown at $-10^{\circ}\mathrm{C}$, while the temperature dependence corresponds to simulations at $V_{dd}=1.2$ V.
  • Figure 5: Irradiation experimental setup and measurement layout: (a) irradiation setup with X-ray tube generator and cooling system at IM2NP. (b) measuring system layout showing connections, sensors, and data acquisition systems.
  • ...and 2 more figures