Photosensitive Full-Swing Multi-Layer MoS₂Inverters With Light Shielding Layers

Photosensitive Complementary Inverters Based on n‐Channel MoS2 and p‐Channel MoTe2 Transistors for Light‐to‐Frequency Conversion Circuits

“…As the wavelength under light illumination decreases from dark to blue ( λ = 450 nm), performance degradation is observed even for saturation characteristics due to the increase in electron–hole pair generation in MoS 2 FETs, which leads to reduction in inverter gains. All the results for MoS 2 FETs were perfectly matched with those of the previously reported results . In contrast, Figure b,d shows transfer characteristics for MoTe 2 under darkness and illumination, illustrating that the photoleakage current level depending on the exposed wavelength was negligibly observed.…”

“…In this sense, for better immunity on external noise for the IoT sensor application, light‐to‐frequency conversion (LFC) circuits could be one of the core elements. Thus, beyond simple photodetectors in the passive mode, photosensitive inverter schemes that can be applicable toward LFCs were recently reported using several different configurations: 1) a‐Si thin film transistor (TFT)‐based pseudo‐depletion load scheme; ii) photosensitive molybdenum disulfide (MoS 2 ) inverters with light shield layers; iii) photosensitive inverter schemes with a MoS 2 load and a GaN driver; and other configurations. Thus, with the reported schemes based on photosensitive MoS 2 loads, energy bandgap ( E g ) modulation depending on the number of MoS 2 layers and its light detection with different wavelengths according to E g were conceptually demonstrated.…”

“…Thus, with the reported schemes based on photosensitive MoS 2 loads, energy bandgap ( E g ) modulation depending on the number of MoS 2 layers and its light detection with different wavelengths according to E g were conceptually demonstrated. Furthermore, noise immunity for the newly reported photodetectors can be dramatically improved as compared with both conventional photodiodes and only n‐ (or p‐) type transistors. In addition, chip density and circuit complexity can be significantly improved via the MoS 2 ‐based LFC scheme, owing to a simple principle of ring oscillators (ROs), as compared with a complicated phase‐locked loop (PLL) system.…”

“…The conventional PLL system contains an optical detector that is composed of a voltage‐controlled RO, a photodiode, a low pass filter, a loop filter, and others . However, the previously reported schemes have fundamental limitations on power consumption because they are implemented using only negative‐channel metal–oxide–semiconductor (NMOS) logic, which is composed of a pseudo‐depletion NMOS load and an NMOS driver. Thus, for the improvement of power consumption in LFCs based on TMDCs, the adoption of photosensitive complementary inverters and their application toward LFCs are highly recommended.…”

“…In this sense, superficially photoinsensitive properties of MoTe 2 FETs have strong advantages for the implementation of photosensitive inverters and their applications in LFCs due to the simplicity of the fabrication scheme. In contrast, photosensitive NMOS inverters, composed of either a‐Si or MoS 2 , need additional process steps (or layers) to physically block light illumination in the area of driver transistors during the fabrication process. Otherwise, as an alternative scheme, photoinsensitive active layers under visible light illumination are necessary, leading to incorporating with heterogeneous active layers such as GaN or SiC, which did not perfectly match with the TMDC fabrication process.…”