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HitPix3 -- a new HV-CMOS active pixel sensor for ion beam therapy

Hui Zhang, Bogdan Topko, Ivan Perić

TL;DR

HitPix3 addresses the need for real-time, high-rate, radiation-tolerant beam monitors in ion-beam therapy by implementing a monolithic HV-CMOS sensor with per-pixel hit counting, on-sensor beam projection, and dual readout modes. The approach combines a 180 nm HV-CMOS process on high-resistivity substrate, deep-n-well isolation, a modified amplifier, per-pixel threshold tuning, and a fast adder-based readout to deliver 2D beam projections with low latency. Key contributions include the integration of an 8-bit counter and 14-bit adder per pixel, a local per-pixel threshold tuning (TuneDAC) to reduce threshold dispersion by >4×, and a faster 190 Mbit/s readout compared with prior HitPix generations, validated on unirradiated devices up to −180 V. The work demonstrates a scalable, low-material, high-rate beam monitor suitable for MRI-guided ion therapy and lays the groundwork for assembling a full 26 cm × 26 cm sensitive area using multiple HitPix3 dies, moving toward a 2 cm × 2 cm die in a 13 × 13 sensor matrix for HIT applications.

Abstract

Particle therapy is a well-established clinical treatment of tumors and so far, more than one hundred centers are in operation around the world. High accuracy on position and dose rate in beam monitoring are major cornerstones of clinical success in particle therapy. A high voltage CMOS (HV-CMOS) monolithic active pixel sensor was developed for this beam monitoring system. The HV-CMOS technology has demonstrated many advantages over other technologies in dealing with radiation tolerance. This HV-CMOS sensor was produced with a 180 nm commercial technology on high-resistivity substrate. The HitPix sensor features several specific design details for operation in a high-intensity ion beam environment: hit-counting pixels, on-sensor projection calculation, radiation tolerant design and frame-based readout. It has a 9775 $μ$m $\times$ 10110 $μ$m sensor area with 200 $μ$m $\times$ 200 $μ$m pixel size. The new HitPix3 has a number of improvements, including a modified in-pixel amplifier, on-sensor calculation of beam profile projection in two dimensions, and in-pixel threshold tuning capacity. The functionality of these features was confirmed in laboratory tests of unirradiated HitPix3 sensors, making the HitPix3 an important step in developing a sensor for use in ion beam monitoring.

HitPix3 -- a new HV-CMOS active pixel sensor for ion beam therapy

TL;DR

HitPix3 addresses the need for real-time, high-rate, radiation-tolerant beam monitors in ion-beam therapy by implementing a monolithic HV-CMOS sensor with per-pixel hit counting, on-sensor beam projection, and dual readout modes. The approach combines a 180 nm HV-CMOS process on high-resistivity substrate, deep-n-well isolation, a modified amplifier, per-pixel threshold tuning, and a fast adder-based readout to deliver 2D beam projections with low latency. Key contributions include the integration of an 8-bit counter and 14-bit adder per pixel, a local per-pixel threshold tuning (TuneDAC) to reduce threshold dispersion by >4×, and a faster 190 Mbit/s readout compared with prior HitPix generations, validated on unirradiated devices up to −180 V. The work demonstrates a scalable, low-material, high-rate beam monitor suitable for MRI-guided ion therapy and lays the groundwork for assembling a full 26 cm × 26 cm sensitive area using multiple HitPix3 dies, moving toward a 2 cm × 2 cm die in a 13 × 13 sensor matrix for HIT applications.

Abstract

Particle therapy is a well-established clinical treatment of tumors and so far, more than one hundred centers are in operation around the world. High accuracy on position and dose rate in beam monitoring are major cornerstones of clinical success in particle therapy. A high voltage CMOS (HV-CMOS) monolithic active pixel sensor was developed for this beam monitoring system. The HV-CMOS technology has demonstrated many advantages over other technologies in dealing with radiation tolerance. This HV-CMOS sensor was produced with a 180 nm commercial technology on high-resistivity substrate. The HitPix sensor features several specific design details for operation in a high-intensity ion beam environment: hit-counting pixels, on-sensor projection calculation, radiation tolerant design and frame-based readout. It has a 9775 m 10110 m sensor area with 200 m 200 m pixel size. The new HitPix3 has a number of improvements, including a modified in-pixel amplifier, on-sensor calculation of beam profile projection in two dimensions, and in-pixel threshold tuning capacity. The functionality of these features was confirmed in laboratory tests of unirradiated HitPix3 sensors, making the HitPix3 an important step in developing a sensor for use in ion beam monitoring.

Paper Structure

This paper contains 19 sections, 19 figures, 1 algorithm.

Table of Contents

  1. Introduction
  2. A beam monitor based on an HV-CMOS Sensor
  3. Sensor design
  4. Pixel electronics
  5. Charge sensitive amplifier
  6. TuneDAC
  7. Feedback Boost
  8. Counter and adder
  9. Pixel layout
  10. Sensor peripheral electronics
  11. Measurements
  12. I-V measurement
  13. Latency scan measurement
  14. CSA calibration measurement
  15. Charge injection measurement
  16. ...and 4 more sections

Figures (19)

  • Figure 1: Cross-section illustrating the HV-CMOS technology Zhang2022_phd.
  • Figure 2: Modified HV-CMOS sensor designed with a deep p-well implant Zhang2022_phd.
  • Figure 3: Simplified block diagram of the HitPix3 sensor.
  • Figure 4: Schematic of pixel electronics.
  • Figure 5: Feedback circuit with the boost feature (red box).
  • ...and 14 more figures