This paper presents an overview of silicon-based optical sensors for the measurement of light in the visible spectrum range. The review is focused on sensors based on CMOS (complementary metal-oxide semiconductor) technology due to the high availability, low cost, ease of prototyping, and well-established fabrication processes. CMOS technology allows integration with the CMOS readout and control electronics in the same microdevice, featuring high-volume fabrication with high-reproducibility and low-cost. This review starts with an explanation of the phenomena behind opto-electronic transduction. It also presents and describes the most common components responsible for optical transduction, readout electronics, and their main characteristics. This review finishes with the presentation of selected applications to grasp where and how these sensors can be used.

Objectives: Optical spectrophotometry has been explored to quantify Plasmodium falciparum malaria parasites at low parasitemia, with potential to overcome the limitations of detection in the current diagnostic methods. This work presents the design, simulation and fabrication of a CMOS microelectronic detection system to automatically quantify the presence of malaria parasites in a blood sample. Methods: The designed system is composed by an array of 16 n+/p-substrate silicon junction photodiodes as photodetectors and 16 current to frequency (IF) converters. An optical setup was used to individually and jointly characterize the entire system. Results: The IF converter was simulated and characterized in Cadence Tools using UMC 1180 MM/RF technology rules, featuring a resolution of 0.01 nA, a linearity up to 1800 nA and a sensitivity of 4430 Hz/nA. After fabrication in a silicon foundry, the photodiodes' characterization presented a responsivity peak of 120 mA/W (λ = 570 nm) and a dark current of 7.15 pA at 0 V. Regarding the IF converter, it exhibited high linearity (R ² ≈ 0.999) up to 30 nA, with a sensitivity of 4840 Hz/nA. Furthermore, the microsystem performance was validated using RBCs (Red Blood Cells) infected with P. falciparum and diluted at different parasitemia (12, 25 and 50 parasites/μL). Conclusion: The microsystem was able to distinguish between healthy and infected RBCs, with a sensitivity of 4.5 Hz/parasites.μL ^-1 . Significance: The developed microsystem presents a competitive result, when compared to the gold standard diagnosis methods, with increased potential for malaria in field diagnosis.

Accurate pH sensing is essential for the effective physiological control of the culture media in organ-on-a-chip (OoC) systems. This work proposes a miniaturized optical detection system, based on optical transmittance, for pH level quantification of the EGM™-2 Endothelial Cell Growth Medium-2 BulletKit™ culture medium. Firstly, using a commercial spectrophotometric setup, a set of wavelengths (500, 560, and 600 nm) was selected, as these wavelengths assure distinctive slope variations for the different pH levels. Then, a current-to-frequency converter, based on a low-power Schmitt trigger model with a voltage enhancer, was proposed as the readout electronics and simulated in Cadence Tools using UMC L180 MM/RF technology. A resolution of 0.002 nA was achieved in the linear range of 30 pA to 3800 nA. A miniaturized system composed of a CMOS n-well/p-substrate photodiode and a polydimethilsiloxane (PDMS) microchannel for the culture media substrate was experimentally tested. For a pH range from 6.6 to 6.2, the results clearly demonstrate a magnitude shift of the slope signal, which becomes negative in basic media and positive in acidic media. Additionally, in the 500–560 nm spectral range, the amplitude of the slopes increases for both basic and acidic culture media. In the 560–600 nm range, the slope decreases progressively as the pH of the medium lowers. This miniaturized system was able to quantify the pH of the culture medium, showing potential to be integrated into an organ-on-a-chip device.

Reliable temperature monitoring remains a critical bottleneck in Organ‐on‐a‐Chip (OoC) systems, where integrated temperature sensors must provide electrical stability, biocompatible encapsulation, and efficient thermal coupling to the biological environment. While the effects of thermal annealing on platinum (Pt) thin films are well established, the influence of fabrication‐related thermal budgets associated with OoC manufacturing has not been systematically correlated with device performance. Here, we establish a direct processing–microstructure–device performance relationship for Pt‐based resistance temperature detectors (RTD). Using Si/Pt and Si/SiO ₂ /Pt architectures, we investigate the impact of thermal annealing (up to 900°C) on film morphology and electrical properties and correlate them with device‐level sensing performance. Moderate annealing temperatures (≈300°C), representative of oxide passivation processes, significantly improve electrical performance, reducing resistivity by up to 40% and increasing the temperature coefficient of resistance (TCR) through stress relaxation and grain coarsening. Higher annealing temperatures induce surface roughening and morphological instability, compromising sensor reliability. A SiO ₂ interlayer delays degradation and reduces resistivity drift, preserving film integrity under harsh thermal conditions. These results demonstrate that the thermal budget associated with dielectric passivation can be exploited to optimize RTD performance while defining practical processing windows for reliable integration into OoC and other biointegrated microsystems.

Accurately predicting how incident light propagates through complex dielectric layers is essential for optimizing the design and performance of integrated CMOS (Complementary Metal Oxide Semiconductor) silicon photodiodes without relying on additional costly fabrication processes. To address this need, this work presents a comparative analysis between three numerical approaches for modelling the optical transmission through planar multilayer dielectric stacks, representative of TSMC (Taiwan Semiconductor Manufacturing Company) 65 nm and TSMC 180 nm CMOS technologies. Wave Optics and Ray Optics, implemented in COMSOL Multiphysics, together with the transfer-matrix method implemented in TFCalc, were evaluated by comparing spectral transmittance over the 400 to 1000 nm wavelength range, sensitivity to fabrication process-induced thickness variations, angular responses from 0° to 80°, and computational efficiency. The three methods exhibited excellent agreement, accurately reproducing the interference behavior of both dielectric stacks. The TSMC 65 nm technology showed a more complex optical response, whereas the TSMC 180 nm stack presented generally higher transmittance, above 31% throughout the evaluated spectral range. Process tolerances primarily shifted the spectral position of the interference peaks by approximately 90 nm and 80 nm, for TSMC 65 nm and 180 nm technologies respectively, without significantly altering the overall spectral behavior, while angular averaging from 0° to 60° smoothed the transmittance oscillations expected under practical LED (Light-Emitting Diode) illumination. TFCalc achieved near full-wave accuracy while reducing the computational time from nearly four hours to approximately one second, demonstrating the best accuracy–efficiency trade-off for planar multilayer dielectric stack analysis in CMOS photodiode design.