研究目的
To study the depletion depth in CMOS pixel sensors using a frontside biasing technique, specifically investigating the evolution of depletion depth with bias voltage on high resistivity substrates for applications in particle tracking and X-ray detection.
研究成果
The frontside biasing technique enables full depletion of thin epitaxial layers (up to 13 μm at 30 V bias) and partial depletion of bulk substrates (up to 17 μm at 40 V bias), with effective charge collection beyond the depleted volume in bulk substrates. This method is promising for applications in particle tracking and X-ray detection, with further studies needed for optimization and validation with charged particles.
研究不足
The analytical model is simplified and may not fully capture real sensor geometries, especially for high resistivities. TCAD simulations are computationally intensive and based on specific assumptions. Experimental estimates rely on reference depths from simulations and may be affected by uncertainties in X-ray rates and detection efficiencies. The study is limited to specific substrate types and bias voltages up to 45 V.
1：Experimental Design and Method Selection:
The study uses a frontside biasing technique for CMOS pixel sensors, involving analytical modeling (simplified point-like diode model) and 3D-TCAD simulations to predict depletion depth. Experimental validation is performed using X-ray illumination to measure depletion depths.
2：Sample Selection and Data Sources:
Sensor prototypes (PIPPER-2) fabricated on two substrates: an 18 μm thick high resistivity epitaxial layer (HR18, >1 kW cm) and a thinned bulk substrate (CZ, 600 W cm, thinned to 40 μm sensitive depth). X-ray sources include a 55Fe source (5.89 keV) and a Rigaku D/MAX-B X-ray generator with monochromator (17.48 keV).
3：89 keV) and a Rigaku D/MAX-B X-ray generator with monochromator (48 keV).
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: PIPPER-2 CMOS pixel sensor prototypes, high voltage biasing setup, X-ray sources (55Fe and Rigaku D/MAX-B), external 14-bit analog-to-digital converter for signal digitization, and computational tools for TCAD simulations (Synopsys TCAD).
4：Experimental Procedures and Operational Workflow:
Apply reverse bias voltages (up to 45 V) to sensors, illuminate with X-rays, acquire frames (3,000,000 per bias voltage), perform clustering analysis to identify X-ray hits, and analyze charge distributions to estimate depletion depths using count ratios based on Beer-Lambert law.
5：Data Analysis Methods:
Use analytical models and TCAD simulations for predictions. Experimental data analyzed by fitting full-energy peaks and integrating counts, with depletion depth calculated from attenuation coefficients and reference depths derived from simulations.
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