Lateral coupling and immunity to substrate effect in ΩFET devices

The inter-gate coupling effects in multiple-gate SOI devices with Omega configuration, metal gate and HfO2 dielectric are investigated. Electrical measurements together with 3D numerical simulations show that the back-gate influence is reduced for narrow devices due to a strong lateral coupling between the two lateral sides of the main gate. In spite of the full depletion of the transistor body, the threshold voltage and the subthreshold slope are no longer dependent on the back gate bias. It is also shown that the conduction channels can be separated in wide ΩFETs using the back-gate coupling in accumulation mode. DIVSB (drain-induced virtual substrate biasing) can be drastically reduced when the lateral coupling screens the drain influence. Narrow devices are then virtually immune to substrate effects.