Global shutter quantum dot image sensor for NIR imaging

L. Baudoin et al. of  ISAE SUPAERO, University of Toulouse, Toulouse, France recently published a paper titled "Global Shutter and Charge Binning With Quantum Dots Photodiode Arrays for NIR Imaging" in the IEEE Journal of the Electron Devices Society.

Open access link: https://ieeexplore.ieee.org/document/10742005

Abstract:  New applications like depth measurements or multispectral imaging require to develop image sensors able to sense efficiently in the Near Infrared and Short-Wave Infrared where silicon is weakly sensitive. Colloidal Quantum Dots (CQD) technology is an interesting candidate to address these new applications as it allows to develop image sensors with high quantum efficiency at excitonic peak and high-resolution images. In this paper, we present an electrical model describing the electrical behavior of a designed and manufactured CQD photodiode. We use this model to explore a different architecture collecting holes instead of electrons. This architecture allows to control the charge collection inside the CQD thin film through the electric field. This property enables to implement global shutter functionality, to bin charges from several photodiodes, or to operate two physically interleaved photodiodes arrays alternatively with different types of pixel circuitries. These operating modes extend the capabilities of CQD image sensors in terms of applications.

Overview of the CQD thin film properties.

(a) Electron microscopy cross section of the characterized photodiode [16] (b) Scheme of the simulated device for electrons collection (c) CQD photodiode process flow [16].

(a) CQD photodiode absorption spectrum (b) Current vs Voltage CQD photodiode characteristic – experiment vs simulation.

(a) Scheme of the simulated device for holes collection (b) Band diagram of the photodiode varying the voltage of the bottom electrode (c) Physical phenomena explaining the photodiode current vs voltage characteristic.

Current vs Voltage characteristics vs (a) CQD thin film holes mobility (b) carriers lifetime (c) CQD thin film electron affinity (d) ETL electron affinity (e) HTL electron affinity Turn-on bias vs (f) CQD thin film holes mobility (g) carriers lifetime (h) CQD thin film electron affinity (i) HTL electron affinity.

(a) Scheme of the multi-electrodes device working principle (b) Multi-electrodes photodiode architecture for holes collection control alternating collection on pixels A (top image) and collection on pixel B (bottom image).

Electrostatic potential and band diagrams explaining the carriers’ collection control for: (a) electrons collecting photodiodes (b) holes collecting photodiodes.

Current-Voltage characteristics explaining the carriers’ collection control for: (a) electrons collecting photodiodes (b) holes collecting photodiodes.

Electric field for photodiodes with central bottom electrode biased and various bottom electrodes’ widths.

Turn-on bias vs work functions for various electrodes’ size.

 

Current-Voltage characteristics of the collecting and non-collecting electrodes at various illuminations.