The millimeterwave (MMW) and terahertz (THz) frequency spectrum of electromagnetic waves have attracted significant interest in science and engineering. The advances in active and passive Monolithic Microwave Integrated Circuit (MMIC) technology have opened up opportunities for new applications such as ultra-fast wireless point-to-point communication, miniaturized high-resolution imaging radar for collision avoidance and navigation, as well as environmental and biomedical applications.
An advantage of the SMMW frequency range is the availability of wide non-restricted bandwidth. However, there are many challenges that need to be overcome to fully exploit this band of electromagnetic wave spectrum. One major issue pertains to the difficulty in fabrication of transmission lines needed for realization of passive components such as filters, couplers, power dividers and interconnects. Another issue is related to the complexity associated with measurement and characterization of components and RF sub-systems. Due to low loss and high power handling characteristics, rectangular waveguides seem to be the appropriate choice. Another advantage of rectangular waveguides is their compatibility with silicon micromachining, allowing accurate microfabrication of different waveguide based components and devices such as antennas, filters, power dividers and waveguide to planar lines transitions.
However, measurement of S-parameters of micromachined on-wafer components is not straightforward. At lower frequencies (up to G-band), coaxial and coplanar waveguide (CPW) line ground–signal–ground (GSG) probes are commonly used for on-wafer S-parameter measurements. However, at frequencies above G-band the dimensions of the coaxial lines and the probe tips become too small to be mechanically stable. Larger size coaxial probes and probe tips lead to excitation of higher order modes in the line and radiation from the probe tips. Also the parasitics from the probe tips and the pads on the wafer lead to unreliable and non-repeatable measurements.
A non-contact on-wafer S-Parameter measurements of devices at millimeter-wave to terahertz frequencies
The proposed technology is a novel method for reliable and repeatable characterization of devices and chips at MMW and higher frequency ranges. This technology is based on using open-ended waveguide probes along with novel probe to on-wafer waveguide transitions to measure the S-parameters of active and passive components and devices. To enable non-contact measurements, an RF choke is devised on the metallic cross section of the probes using electric discharge machining. Additionally, to enhance the accuracy and repeatability of the measurements, a novel probe aligner is micromachined over the on-wafer transition. This setup enables reliable RF characterization of active and passive components and devices. In order to perform MMIC characterization, new waveguide to co-planar waveguide (CPW) transitions are incorporated in the design. Also, a thru-wafer chip integration technology is developed to enable accurate alignment of the MMIC chip with the on-wafer CPW lines. Conductive pillars are devised on the RF and DC pads to ensure the physical contact between the lines on the MMIC chip and the on-wafer lines.
- A repeatable and reliable method for characterization of on-wafer devices as well as active and passive MMIC chips at MMW and THz frequencies.
- Communications sectors like remote sensing, RADAR, LiDAR, etc.
- Weapon systems using millimeter wave radar
- Security screening in airports using millimeter wave scanners
- Enabling accurate characterization of S-parameters of multi-port active and passive components at submillimeter wave to THz band.
- Reducing the cost of the high frequency on-wafer measurements
- Eliminating the need for assembly of multiple parts in current state of the art probes