Cosan Caglayan

Non-Contact Probes for On-Wafer Characterization of Sub-Millimeter-Wave Devices and Integrated Circuits

We present a novel non-contact metrology approach for on-wafer characterization of sub-millimeter-wave devices, components, and integrated circuits. Unlike existing contact probes that rely on small metallic tips that make physical contact with the device on the chip, the new non-contact probes are based on electromagnetic coupling of vector network analyzer (VNA) test ports into the coplanar waveguide environment of integrated devices and circuits. Efficient signal coupling is achieved via a quasi-optical link between the VNA ports and planar antennas that are monolithically integrated with the test device. Experimental validation of the non-contact device metrology system is presented for the first time to demonstrate the accuracy and repeatability of proposed approach for the 325-500-GHz (WR2.2) and 500-750-GHz (WR1.5) bands.

Lumped-Element Equivalent-Circuit Modeling of Millimeter-Wave HEMT Parasitics Through Full-Wave Electromagnetic Analysis

We present a broadband lumped-element parasitic equivalent circuit to accurately capture the frequency response of electromagnetic (EM) interactions inside the structure and surrounding environment of high electron-mobility transistors (HEMTs). A new mutual inductance term is included to account for the high-frequency magnetic field coupling between device electrodes. An analytical method is also proposed, for the first time, to extract the gate-to-drain mutual inductance LMGD, which creates an undesirable inductive feedback path from output to input at millimeter wavelengths. Based on the suggested extrinsic equivalent circuit, we propose a novel multistep parameter extraction procedure that utilizes direct analytic extraction and linear regression techniques systematically to determine the parasitic component values. The accuracy and robustness of the presented extraction algorithm are established via comprehensive comparisons between EM simulations, measurements, and frequency responses of the suggested equivalent circuits up to and beyond 300 GHz in the millimeter-wave (mmW) band. The key parasitic elements that are most detrimental to the microwave performance are identified and optimized through subsequent circuit analysis. Design guidelines are provided for optimum device layout selection to achieve the highest frequency performance. It is demonstrated through a full-wave simulation based parametric study that around 20% improvement in maximum oscillation frequency is achievable via optimization of device gate finger number and unit finger width.

Non-contact probes for device and integrated circuit characterization in the THz and mmW bands

We present a novel, non-contact, on-wafer device characterization method covering both THz (300 GHz-3 THz) and mmW bands (60-300 GHz). Unlike existing contact probes which rely on fragile tips and physical contact with the device on the chip, the new non-contact probe setup is based on radiative coupling of vector network analyzer test ports into the coplanar waveguide environment of monolithic devices and integrated circuits via planar, on-chip, broadband antennas. The on-chip antennas act as “virtual” probe-tips on the test wafer and connect to the device through optimized, impedance matched coplanar waveguide (CPW) lines. Proof-of-concept validation is presented for the 325-750 GHz band using WR2.2 and WR1.5 frequency extender modules and a standard vector network analyzer as the backend. Owing to the non-contact nature, these new probes are free from wear/tear and fragility issues. More importantly, they are low cost and can be easily scaled beyond 900GHz where there is no existing solution for on-wafer device and integrated circuit testing.

On-wafer device characterization with non-contact probes in the THz band

We present a novel approach for on-wafer device characterization in the THz band. A non-contact method eliminating the need for physical contact with test wafer is proposed. Non-contact method is based on radiative coupling of Network Analyzers test ports into coplanar environment of monolithic device (DUT) through integrated planar THz antennas. Broadband butterfly-shaped antennas are used to ensure that the characterization setup is not limited by the bandwidth of the non-contact probes. Calibration is carried out using open and short terminations with different lengths. Initial results based on the full wave simulations demonstrate the broadband and efficient coupling capability of non-contact THz probes as well as the functionality of different terminations for calibration purposes.

Non-contact differential-mode on-wafer device characterization in the mmW and THz bands

We present a novel on-wafer metrology technique for characterization of differential Millimeter-wave and Terahertz Monolithic Integrated Circuits (MMIC and TMICs) using a contact-free setting that relies on quasi-optical coupling of test signals onto the device on chip. Due to their advantages over single-ended topologies, differential circuits are typically preferred, particularly for superior noise performance. However, lack of characterization equipment at sub-mmW frequencies severely inhibits the proliferation of differential MMIC and TMICs. Currently, balun-integrated wafer contacting probes are most commonly used for mixed mode S-parameter measurements. Nevertheless, these probes are commercially available only up to 110 GHz with prototypes proposed up to 140 GHz. In this paper, initial validation of novel, non-contact, differential-mode on-wafer probes is presented with validations for the 220-325 GHz.

Repeatability performance of non-contact probes in the 500–750GHz band

We present the repeatability performance of an automated non-contact probe system for on-wafer device and integrated circuit characterization in the 500-750 GHz band. Unlike conventional contact-probe systems, a computer controlled x-y translation stage is employed to realize a completely automated non-contact probe setup. Thanks to this simplicity, far superior repeatability performance can be achieved with great ease. We present the repeatability study specifically for the 500-750 GHz band utilizing a precision servo system with 1 micron translation accuracy. At 625 GHz, our setup achieves 2.2° deviation in phase and 4.4% deviation in magnitude for 25 successive measurements spanning over 1.5 hours. This fully computerized non-contact probe system also facilitates intermittent re-calibrations that are normally needed for reliable sub-mmW measurements.

Experimental Analysis of Repeatability and Calibration Residuals in On-Wafer Non-Contact Probing

We experimentally demonstrate the repeatability performance of non-contact probes for millimeter-wave (mmW) and terahertz (THz)-frequency on-wafer device characterization under typical laboratory settings. Akin to conventional contact probe measurements, the leading contribution to the overall uncertainty of non-contact measurements in mmW and THz bands is due to mechanical alignment repeatability that cannot be removed through on-wafer calibration. Nevertheless, measurement uncertainty for non-contact probes studied here through one-port and two-port measurements conducted in 140–750 GHz bands demonstrate excellent S-parameter measurement repeatability, as predicted by full-wave simulations, and is limited only by instrumentation drift.

On-chip “baluntennas” for differential-mode non-contact characterization of mmW/THz devices and ICs

We present a novel on-chip, lens-integrated differential-mode double-slot antenna structure to enable iso-lated, pure differential-mode signal injection and interrogation for on-wafer devices and integrated circuits. Testing of on-chip differential devices and circuits conventionally requires Marchand-type baluns integrated either with the device or with the dual-tip contact-probes. Nevertheless, these state-of-the-art balun-integrated probes can cover only up to 110 GHz. In this work, we demonstrate a 180°-hybrid “baluntenna” based on a novel on-chip antenna design that concurrently acts as a high isolation balun. The baluntenna is integrated with the device-under-test and a quasi-optical link is used to effectively couple test signals into and out of the on-wafer ports of the device under test. As such, this approach allows, for the first time, non-contact, pure differential-mode characterization of on-chip devices and integrated circuits at well beyond 100 GHz.

Noncontact On-Wafer Characterization of Differential-Mode Millimeter- and Submillimeter-Wave Devices and Integrated Circuits

We present a balun-free, pure differential-mode noncontact measurement technique for on-wafer characterization of devices and integrated circuits (ICs). We demonstrate the validity of this novel approach in the H -band (220-325 GHz), where there are currently no available alternatives. To date, realization of differential-mode millimeter-wave and submillimeter-wave devices and ICs have been hindered by the lack of characterization tools. With the presented approach, we demonstrate a simple, noncontact and cost effective technique that enables much needed differential-mode metrology capability for current and future high-speed electronic systems.

Distributed modeling of submillimeter-wave HEMT parasitics based on full-wave electromagnetic analysis

We present a broadband distributed parasitic equivalent circuit model to accurately reproduce the frequency response of electromagnetic (EM) field couplings within the structure of submillimeter-wave (sub-mmW) high electron mobility transistors (HEMTs) in terahertz (THz) band. We also develop a novel systematic multi-step parameter extraction algorithm. The accuracy of the suggested extraction procedure is validated through extensive comparisons between full-wave (FW) simulated, measured, and modeled frequency responses of the presented test standards up to 750 GHz.