Near-field scanning microwave microscope for interline capacitance characterization of nanoelectronics interconnect

We have developed a noncontact method for measurement of the interline capacitance in Cu/low-k interconnect. It is based on a miniature test vehicle with net capacitance of a few femto-Farads formed by two 20-\mu m-long parallel wires (lines) with widths and spacings the same as those of the interconnect wires of interest. Each line is connected to a small test pad. The vehicle impedance is measured at 4 GHz by a near-field microwave probe with 10 \mu m probe size via capacitive coupling of the probe to the vehicle's test pads. Full 3D finite element modeling at 4 GHz confirms that the microwave radiation is concentrated between the two wires forming the vehicle. An analytical lumped element model and a short/open calibration approach have been proposed to extract the interline capacitance value from the measured data. We have validated the technique on several test vehicles made with copper and low-k dielectric on a 300 mm wafer. The vehicles interline spacing ranges from 0.09 to 1 \mu m and a copper line width is 0.15 \mu m. This is the first time a near-field scanning microwave microscope has been applied to measure the lumped element impedance of a test vehicle

Microwave Electrodynamics of the Antiferromagnetic Superconductor GdBa_2Cu_3O_{7-\delta}

The temperature dependence of the microwave surface impedance and conductivity are used to study the pairing symmetry and properties of cuprate superconductors. However, the superconducting properties can be hidden by the effects of paramagnetism and antiferromagnetic long-range order in the cuprates. To address this issue we have investigated the microwave electrodynamics of GdBa_2Cu_3O_{7-\delta}, a rare-earth cuprate superconductor which shows long-range ordered antiferromagnetism below T_N=2.2 K, the Neel temperature of the Gd ion subsystem. We measured the temperature dependence of the surface resistance and surface reactance of c-axis oriented epitaxial thin films at 10.4, 14.7 and 17.9 GHz with the parallel plate resonator technique down to 1.4 K. Both the resistance and the reactance data show an unusual upturn at low temperature and the resistance presents a strong peak around T_N mainly due to change in magnetic permeability.Comment: M2S-HTCS-VI Conference Paper, 2 pages, 2 eps figures, using Elsevier style espcrc2.st

Noncontact electrical metrology of Cu/low-k interconnect for semiconductor production wafers

We have demonstrated a technique capable of in-line measurement of dielectric constant of low-k interconnect films on patterned wafers utilizing a test key of ~50x50 \mu m in size. The test key consists of a low-k film backed by a Cu grid with >50% metal pattern density and <250 nm pitch, which is fully compatible with the existing dual-damascene interconnect manufacturing processes. The technique is based on a near-field scanned microwave probe and is noncontact, noninvasive, and requires no electrical contact to or grounding of the wafer under test. It yields <0.3% precision and 2% accuracy for the film dielectric constant

A near-field scanned microwave probe for spatially localized electrical metrology

We have developed a near-field scanned microwave probe with a sampling volume of approximately 10 micron in diameter, which is the smallest one achieved in near-field microwave microscopy. This volume is defined to confine close to 100 percent of the probe net sampling reactive energy, thus making the response virtually independent on the sample properties outside of this region. The probe is formed by a 4 GHz balanced stripline resonator with a few-micron tip size. It provides non-contact, non-invasive measurement and is uniquely suited for spatially localized electrical metrology applications, e.g. on semiconductor production wafers.Comment: 6 pages, 3 figures, submitted to Appl. Phys. Let

Synchronous Chip-to-Chip Communication with a Multi-Chip Resonator Clock Distribution Network

Superconducting digital circuits are a promising approach to build packaged-level integrated systems with high energy-efficiency and computational density. In such systems, performance of the data link between chips mounted on a multi-chip module (MCM) is a critical driver of performance. In this work we report a synchronous data link using Reciprocal Quantum Logic (RQL) enabled by resonant clock distribution on the chip and on the MCM carrier. The simple physical link has only four Josephson junctions and 3 fJ/bit dissipation, including a 300 W/W cooling overhead. The driver produces a signal with 35\,GHz analog bandwidth and connects to a single-ended receiver via 20 $\Omega$ Nb Passive Transmission Line (PTL). To validate this link, we have designed, fabricated and tested two 32$\times$32 mm$^2$ MCMs with eight 5$\times$5 mm$^2$ chips connected serially and powered with a meander clock, and with four 10$\times$10 mm$^2$ chips powered with a 2 GHz resonant clock. The meander clock MCM validates performance of the data link components, and achieved 5.4 dB AC bias margin with no degradation relative to individual chip test. The resonator MCM validates synchronization between chips, with a measured AC bias margin up to 4.8 dB between two chips. The resonator MCM is capable of powering circuits of 4 million Josephson junctions across the four chips with a projected 10 Gbps serial data rate.Comment: 8 pages, 8 figure

Microwave Electrodynamics of Electron-Doped Cuprate Superconductors

We report microwave cavity perturbation measurements of the temperature dependence of the penetration depth, lambda(T), and conductivity, sigma(T) of Pr_{2-x}Ce_{x}CuO_{4-delta} (PCCO) crystals, as well as parallel-plate resonator measurements of lambda(T) in PCCO thin films. Penetration depth measurements are also presented for a Nd_{2-x}Ce_{x}CuO_{4-delta} (NCCO) crystal. We find that delta-lambda(T) has a power-law behavior for T<T_c/3, and conclude that the electron-doped cuprate superconductors have nodes in the superconducting gap. Furthermore, using the surface impedance, we have derived the real part of the conductivity, sigma_1(T), below T_c and found a behavior similar to that observed in hole-doped cuprates.Comment: 4 pages, 4 figures, 1 table. Submitted to Physical Review Letters revised version: new figures, sample characteristics added to table, general clarification give

Propagation of Picosecond Pulses on Superconducting Transmission Line Interconnects

Interconnects are a major discriminator for superconducting digital technology, enabling energy efficient data transfer and high-bandwidth heterogeneous integration. We report a method to simulate propagation of picosecond pulses in superconducting passive transmission lines (PTLs). A frequency-domain propagator model obtained from the Ansys High Frequency Structure Simulator (HFSS) field solver is incorporated in a Cadence Spectre circuit model, so that the particular PTL geometry can be simulated in the time-domain. The Mattis-Bardeen complex conductivity of the superconductor is encoded in the HFSS field solver as a complex-conductivity insulator. Experimental and simulation results show that Nb 20 Ohm microstrip PTLs with 1um width can support propagation of a single-flux-quantum pulse up to 7mm and a double-flux-quantum pulse up to 28mm