THz, the electromagnetic spectrum lying between millimeter waves and optics, is nowadays widely utilized in the applications such as material inspection, medicine, explosives detection and astronomy. Although optical and photonic based systems for generating THz waves can fully cover the upper band of the THz spectrum (from several THz to far infrared), they are inefficient at lower frequency bands i.e., mm-waves, and at the same time inappropriately bulky for portable applications. In contrast, recent progress in solid states electronics in conjunction with aggressive scaling of devices are promising to facilitate the future availability of THz systems realized as compact and cheap all-electronic solutions. THz microelectronics is an increasingly relevant field of activities, therefore.
Without concerning about the challenges in the design and fabrication of such devices, their performance needs to be characterized with systems faster than the device itself; therefore, we face with limitations. Recently, the measurement bandwidth of microwave network analyzers equipped with extension modules has extended beyond 1 THz. However, their calibration is a challenging task and performing a full band measurement, due to a need for waveguide components, considerably increases the cost and time of measurement. Systematic errors in system calibration due to lack of precise models for devices at THz frequencies are also remarkable drawbacks of this approach. An eligible alternative for these systems is the use of electrooptic and photoconductive sampling which rely on optical and photonic approaches. These techniques with the help of femtosecond pulse lasers provide a very broadband measurement system far beyond today’s electronic devices bandwidth without suffering from the challenges of the electronic approach. In particular electrooptic sampling with non-contact probing can also perform useful high resolution near field scanning of devices.
The aim of this thesis is to demonstrate the electrooptic sampling for the characterization of mm-wave and THz electronic devices. To this end, an extremely broadband (microwave to THz) device, which is a 65-nm CMOS nonlinear transmission line (NLTL), is used as the device under test. Before showing the measurement results for this device, the advances in THz electronics as well as their common the characterization techniques are reviewed. For the characterization, a rather compact EOS experimental setup featured with a large dynamic range, high sensitivity and high spatial resolution is presented. In the measurement phase, it is shown that what challenges in particular for the characterization of a nonlinear device we may face to and which scenarios can be used to overcome them. The relative jitter in EOS, known as the most prohibiting factor for achieving a high measurement bandwidth, is resolved with a novel synchronization technique called Laser Master Laser Slave (LM-LS). This is achieved by feeding the DUT with a microwave signal which is generated from the comb harmonics of the femtosecond laser. Since the signal is sampled by the laser itself, EOS provides a fully coherent heterodyne detection which helps to significantly increase the detection bandwidth of the system from 50 GHz up to 300 GHz which is presently restricted by the DUT fabrication technology i.e. the 65-nm CMOS. Furthermore, it is shown that for nonlinear devices, measurement with EOS can outperform traditional microwave network analyzer measurements and in particular it can detect hidden features like conversion losses which may not be observed by electronic techniques. In the end by performing photoconductive measurements for the DUT, a good comparison between electrooptic and photoconductive sampling in terms of their detection bandwidth and image resolution is demonstrated.