State-of-the-art measurement instrumentation up to 500 GHz
Propagation constant of a microstrip line against frequency
The frequency limits of the semiconductor device technologies are increased continuously in order to meet the growing demand for bandwidth and data transmission capacity. Electronic circuits already operate at frequencies about 250 GHz and beyond, commonly referred to as terahertz range. The FBH with its state-of-the-art equipment for network and spectrum analysis is well prepared for the challenge of characterizing such devices.
The facilities at FBH include a capable on-wafer measurement system comprising a vectorial network analyzer and an on-wafer probe station. To ensure stability of the system it is located in an air-conditioned laboratory. The network analyzer with its extender modules covers the frequency range up to 500 GHz almost completely. Additionally, a spectrum analyzer is available, which allows measurements up to 750 GHz using mixers. A power meter for the mentioned frequency ranges completes the equipment. Dependent on the frequency range of interest, the devices on the wafers are contacted by coplanar probe tips with coaxial or waveguide interface. The semi-automatic wafer probe station enables a positioning accuracy of 1 µm, which is an indispensable requirement for accurate measurements at small wavelengths. Both the position of the device under test and the distance between the probe tips is adjustable with this accuracy. Since waveguide connections cause high losses in the upper frequency bands, a special inclined mounting of the extender modules was developed in cooperation with the companies Rohde & Schwarz and Radiometer Physics. It minimizes the losses in the measurement system by shortening the connection between the probe tips and the extender modules.
The prerequisite for a reliable measurement is a suitable calibration and error correction. Measurement system and device under test have to be considered as a whole. The standards needed to determine the correction terms shall be established in the same environment as used for subsequent measuring of the devices. For that purpose, standards for the devices to be characterized at FBH are placed directly on the wafer. As an example for the results, the figure shows the propagation constant of a microstrip structure used as standard. The frequency-dependent characteristics provide important insight into the proper performance of the line structure and for the circuit design. For instance, the almost flat curve trace of the relative phase constant in the upper frequency range proves the excellent quasi-TEM properties up to above 300 GHz. In addition, this data enables an evaluation of the calibration quality and the influence of parasitic effects such as higher-order modes.
FBH research: 08.05.2014