PPubMed2 Sep 2008Cited 92×

Monolithic Active Pixel Sensors (MAPS) in a Quadruple Well Technology for Nearly 100% Fill Factor and Full CMOS Pixels

Jamie Alexander Ballin, Jamie Phillip Crooks, Paul Dominic Dauncey, Anne-Marie Magnan, Yoshinari Mikami, Owen Daniel Miller, Matthew Noy, Vladimir Rajovic, Marcel Stanitzki, Konstantin Stefanov, Renato Turchetta, Mike Tyndel, Enrico Giulio Villani, Nigel Keith Watson, John Allan Wilson

Abstract

'Anne-Marie Magnan' 'Yoshinari Mikami' 'Owen Daniel Miller' 'Matthew Noy' 'Vladimir Rajovic' 'Marcel Stanitzki' 'Konstantin Stefanov' 'Renato Turchetta' 'Mike Tyndel' 'Enrico Giulio Villani' 'Nigel Keith Watson' 'John Allan Wilson'] In this paper we present a novel, quadruple well process developed in a modern 0.18 μm CMOS technology called INMAPS. On top of the standard process, we have added a deep P implant that can be used to form a deep P-well and provide screening of N-wells from the P-doped epitaxial layer. This prevents the collection of radiation-induced charge by unrelated N-wells, typically ones where PMOS transistors are integrated. The design of a sensor specifically tailored to a particle physics experiment is presented, where each 50 μm pixel has over 150 PMOS and NMOS transistors. The sensor has been fabricated in the INMAPS process and first experimental evidence of the effectiveness of this process on charge collection is presented, showing a significant improvement in efficiency.

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A new quadruple‑well CMOS process (INMAPS) adds a deep P‑well, letting full‑CMOS pixels keep near‑100% fill factor and boosting charge‑collection efficiency.

What’s new

i.Introduced the INMAPS quadruple‑well process with a deep P‑well implant to isolate N‑wells in standard 0.18 µm CMOS.
ii.Designed and fabricated the TPAC1.0 sensor containing >150 transistors per 50 µm pixel and 28,224 pixels.
iii.Demonstrated experimentally that the deep P‑well raises charge‑collection efficiency from <10% to >20% (up to ~50%).
iv.Showed that full CMOS circuitry can be integrated without significant loss of fill factor, enabling complex in‑pixel processing.

How they did it

The authors modified a standard bulk 0.18 µm CMOS process by adding a deep P‑well implant, designed a sensor (TPAC1.0) with various pixel architectures, simulated charge collection using TCAD, fabricated sensors with and without the deep P‑well, and measured charge collection using a 1064 nm infrared laser focused to 2 µm spots.

What they found

Without deep P‑well, central pixel collected <10% of charge (max ~30%); with deep P‑well, collection was always >20% (max ~50%).
Each pixel consumes ~10 µW power and can be duty‑cycled (2 ms on in a 200 ms period).
The sensor comprises 28,224 pixels over 79.4 mm² with 11.1% dead area.

Caveats

✕The deep P‑well cannot be made very small, limiting applicability to extremely small (<2 µm) pixels.
✕The deep P‑well occupies part of the epitaxial layer, slightly reducing total charge available for collection.
✕Experimental calibration is limited by unknown laser reflections, allowing only relative charge measurements.
✕Results are demonstrated only on the TPAC1.0 prototype; further validation on the upcoming TPAC1.1 is pending.

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