FDSOI Pixel Thesis

CEA-LETI publishes Lina Kadura's PhD Thesis "New FDSOI-based integrated circuit architectures sensitive to light for imaging applications."

"A new type of light sensor called FDPix, composed of one transistor (1T) per pixel is investigated. It consists in co-integrating an FDSOI (Fully-Depleted Silicon-On-Insulator) transistor with a photodiode to enable light sensing through optical back biasing. The absorption of photons and resulting photogenerated charges in the diode will result in a Light Induced VT Shift (LIVS). The LIVS is due to a capacitive coupling between the front and back gate of the FDSOI transistor and represents the key performance metric to be extracted and optimized. In this work, the device behavior in dc and transient domains was thoroughly investigated and modeled. Although not limited to this node, all the devices tested were fabricated using 28nm node FDSOI technology. By means of TCAD simulations and opto-electrical characterization, the device parameters such as Body Factor (BF) and junction profile were optimized to improve its performance. It was found that the FDPix is in fact a dual response sensor. It exhibits a linear response at low light intensity which results in high sensitivity, and a logarithmic response at higher intensities that ensures a high dynamic range (DR) of more than 120dB. The dedicated developed model is implemented in SPICE environment for circuit design. New pixel circuit in analog and digital domain, based on the FDPix were designed, fabricated, and tested. The results obtained and presented in this work, shows the potential of using the FDPix sensor for smart, highly embedded, low power image sensors for More-than-Moore applications."