Inverter Logic of AlGaAs/InGaAs Enhancement/Depletion-Mode Pseudomorphic High Electron Mobility Transistors with Virtual Channel Layers

In this article, the direct-coupled FET logic (DCFL) inverters are implemented by co-integrated AlGaAs/InGaAs depletion-mode and enhancement-mode pseudomorphic high electron mobility transistors with virtual channel layers, and the inverters with varying gate width of the depletion-mode transistors are demonstrated. The experimental results show that the drain current IDS (mA/mm) and gm (mS/mm) per unit gate width increases as the gate widths of the depletion-mode devices decrease. This is attributed to the fact that the drain current and transconductance values are related to the channel-to-source resistance and the source contact resistance. When the gate width is reduced, the source pad contact area is only slightly changed and the IDS (mA/mm) as well as the transconductance gm (mS/mm) will increase. In addition, it is also observed that for the reduce of the gate width of the depletion-mode devices, the transfer characteristics of the DCFL inverters are steep and shift to the left due to the smaller drain saturation current of the load transistor.