An area-efficient 0.5 THz imaging detector in 65-nm CMOS technology

Abstract

Terahertz detector can be used for an imaging detector in terahertz region like as an optical CMOS image sensor. In case of an optical CMOS image sensor (CIS), a unit pixel is generally consisted of a photo diode for receiving a visible ray to contribute to the photocurrent and 4-TRs to transfer the charge. And the unit pixel has been downsized for the higher resolution and the low-cost. Similarly, the terahertz detector uses an antenna to receive the terahertz signal to make a response by using conventional CMOS transistors. However, the terahertz unit pixel needs more chip dimension due to the size of an antenna which occupies most of the chip area when comparing with an optical CMOS image sensor. Additionally, the dimension of the matching elements and tran-sistors is required. Also there still exist a number of challenges and limitations to select proper antenna types since a silicon substrate is not suited for an on-chip antenna in terms of the low resistivity of ~ 10 Ω-cm, and its high dielectric constant of ~11.7. This thesis addresses an area-efficient 0.5 THz imaging detector using a differential patch antenna which is proper to the terahertz imaging system and this structure of the detector is presented that transmission lines, coupling capacitors, and n-type transistors are implemented under the differential patch antenna for saving the chip-dimensions. It is also demonstrated that the matching condition of the antenna in combination with the transmission lines and transistors is verified by measuring the response of the proposed detector in 65-nm CMOS technology. A single pixel achieves a voltage responsivity of 260 V/W and a noise equivalent power (NEP) of 50 pW/ √Hz at 0.5 THz with the device, 60-nm (L) x 2400-nm (W). Finally, terahertz image is shown with a lower noise equivalent power (NEP).