Victor Moro

Achieving real-time and high-resolution photon timing in a compact system remains a key challenge in biomedical sensing and photonics. We present a CMOS SPAD sensor integrating in-pixel analog histogramming for direct fluorescence lifetime acquisition. The 12 × 16 SPAD array features 16-bin analog memories and a tunable delay line with bin widths down to 470 ps. A dual-stage isolation scheme ensures analog stability, achieving average leakage rates of 0.33 mV ms−1 and enabling integration times up to 256 μs without degradation. The sensor was first validated using Alexa Fluor 568 and QDot 705, demonstrating accurate extraction of both short- and long-lifetime decays. It was subsequently evaluated in a compact lens-less platform with QDot 605 and QDot 705, confirming consistent lifetime extraction in a fully integrated configuration. Lifetime extraction was possible using as few as four bins, enabling fast and adaptive acquisition. In-pixel calibration maintains uniform bin linearity, further supporting robust analog histogramming across all temporal configurations. This work establishes a scalable solution for time-resolved fluorescence sensing, with potential for point-of-care diagnostics and compact bioanalytical systems.

Digital histogram generation for time-resolved measurements with single-photon avalanche diode (SPAD) sensors requires the storage of many timestamp signals. This work presents a mixed-signal time-to-digital converter (TDC) that uses analog storage to achieve an area-efficient design that can be integrated in large SPAD arrays. Fabricated using a 150 nm CMOS process, the prototype occupies an area of only 18.3 µm × 36.5 µm, a notable size reduction compared to conventional designs. The experimental results demonstrated high performance, with an integral nonlinearity (INL) of 0.35/0.14 least significant bit (LSB) and a differential nonlinearity (DNL) of 0.14/−0.12 LSB. In addition, the proposed TDC can support the construction of histograms comprising up to 512 bins, making it an effective solution to accommodate a wide range of resolution requirements. Validated in a point-of-care (PoC) device for fluorescence lifetime measurements, it distinguished between lifetimes of approximately 4.1 ns, 3.6 ns and 80 ns with the Alexa Fluor (AF) 546 and 568 dyes and Quantum Dot (QD) 705, respectively. The analog storage design and area-efficient architecture offer a novel approach to integrating TDCs in SPAD-based systems, with potential applications in medical diagnostics and beyond.

A Point-of-Care system for molecular diagnosis (PoC-MD) is described, combining GaN and CMOS chips. The device is a micro-system for fluorescence measurements, capable of analyzing both intensity and lifetime. It consists of a hybrid micro-structure based on a 32 × 32 matrix addressable GaN microLED array, with square LEDs of 50 µm edge length and 100 µm pitch, with an underneath wire bonded custom chip integrating their drivers and placed face-to-face to an array of 16 × 16 single-photon avalanche diodes (SPADs) CMOS. This approach replaces instrumentation based on lasers, bulky optical components, and discrete electronics with a full hybrid micro-system, enabling measurements on 32 × 32 spots. The reported system is suitable for long lifetime (>10 ns) fluorophores with a limit of detection ~1/4 µM. Proof-of-concept measurements of streptavidin conjugate Qdot™ 605 and Amino PEG Qdot™ 705 are demonstrated, along with the device ability to detect both fluorophores in the same measurement.

GaN-on-Si based hybrid microdisplays have been the revolution as point-like light sources for scientific, communications, and imaging applications because of their high-resolution, high-brightness, and high-speed capabilities. Nevertheless, the microdisplay driving circuits usually focus only on two of these characteristics. In this work, we present a CMOS backplane that aims to exploit the capabilities of the GaN-based micro-arrays. The back panel can drive an array of GaN LED pixels of up to 512x512 of 1411 PPI (pixel per inch) with an in-pixel driver that offers a bias current up to 120 μA. The smart pixel control circuit has a 4-bit grayscale resolution. Frames can be updated at up to 10 kfps. Finally, the backplane can be operated in pulsed mode, toggling the entire array between the stored frame and off state at 1 MHz. The backplane design in 180 nm CMOS process and the in-pixel driver simulations results are presented.

Recent research into miniaturized illumination sources has prompted the development of alternative microscopy techniques. Although they are still being explored, emerging nano-light-emitting-diode (nano-LED) technologies show promise in approaching the optical resolution limit in a more feasible manner. This work presents the exploration of their capabilities with two different prototypes. In the first version, a resolution of less than 1 µm was shown thanks to a prototype based on an optically downscaled LED using an LED scanning transmission optical microscopy (STOM) technique. This research demonstrates how this technique can be used to improve STOM images by oversampling the acquisition. The second STOM-based microscope was fabricated with a 200 nm GaN LED. This demonstrates the possibilities for the miniaturization of on-chip-based microscopes.

The recent advances in chip-size microscopy based on optical scanning with spatially resolved nano-illumination light sources are presented. This new straightforward technique takes advantage of the currently achieved miniaturization of LEDs in fully addressable arrays. These nano-LEDs are used to scan the sample with a resolution comparable to the LED sizes, giving rise to chip-sized scanning optical microscopes without mechanical parts or optical accessories. The operation principle and the potential of this new kind of microscope are analyzed through three different implementations of decreasing LED dimensions from 20 µm down to 200 nm.