Per Ohlckers

Packaging of fiber-coupled optoelectronic module for cryogenic voltage standards

The Josephson Arbitrary Waveform Synthesizer (JAWS) is currently being developed for generating precise voltage waveforms, for use in measurement standards. These system is based on superconducting Josephson junction arrays, and are operated by controlling the JAWS with high-speed (>10 GHz) current pulse trains in a cryogenic environment at 4K. Using an optical input rather than an electrical input, has several advantages, including shielding from electromagnetic noise and easier parallel operation of Josephson arrays Therefore, a customized optical input module, where high speed photodiodes converts short optical pulses to current pulses, is being developed. The module consists of multiple lensed InGaAs/InP photodiodes are flip chip bonded to a silicon carrier with gold stud bumps and a customized fiber attachment. Early prototypes showed that chip cracking of the silicon carrier occurred due to thermal stresses caused by the fiber attachment. A technique for assembling multiple optical fibers was developed, using silicon fixtures for mechanically aligning and fixing borosilicate alignment sleeves. In order to simplify assembly, the fixture is aligned by the flip chip technique and adhesively bonded to the carrier with an epoxy. Sufficient alignment accuracy has been achieved, with an average misalignment of 13 μm between the fixture and the photodiode position. Testing of an assembled module showed promising behavior, achieving a stable optical coupling when immersed in liquid Nitrogen and having sufficient strength for operation down to 4 K.

Silicon grass based nano functional electrodes for MEMS supercapacitors of improved energy density

Nano-structure functional electrodes for high energy density MEMS supercapacitors have been fabricated by combining atomic layer deposition (ALD) and cyclic deep reactive ion etch (C-DRIE) in MEMS technology. The electrodes were structured with C-DRIE organized silicon grass (Si-g) as the scaffold for conformal coating with ALD nano-layer TiN as the current collector, and electrochemical loading pseudo-capacitive active material. As obtained Si-g/TiN/MnOx on-chip electrode results in 1) large surface gain scaffold with one dimensional ionic diffusion, 2) high conductivity and electrochemical stability current collector, 3) high effective number of redox centers per volume, which enable largely improved energy density.

Packaging of fiber-coupled module for Josephson junction array voltage standards

This paper describes issues related to the packaging of a fiber coupled optoelectronic module intended as a current source for pulse-driven Josephson arrays, operating at cryogenic temperatures. The module consists of flip-chip bonded photodiodes on a silicon carrier with adhesively bonded optical fiber components in a compact package. Optical and thermomechanical simulations were performed, showing that the needed functionality can be achieved, with optical coupling efficiency above 90% for fiber-chip misalignments up to 40 μm, and that the thermomechanical stresses can be reduced by controlling of the adhesive bonding process.

Development of high precision voltage dividers and buffer for AC voltage metrology up to 1 MHz

A voltage divider and buffer system has been proposed in order to improve the AC Voltage traceability at Justervesenet (JV) for frequencies up to 1 MHz. The buffer is constructed with the intention to drive any heavy load impedance. Simulations suggest that AC-DC difference span less than 30 ppm for frequencies up to 1 MHz for both divider and buffer.

Simulation and development of high precision Voltage dividers and buffer for AC voltage metrology up to 1 MHz

A voltage divider and buffer system has been proposed in order to improve the AC Voltage traceability at Justervesenet (JV) for frequencies up to 1 MHz. Buffer prototypes have been constructed for use at room temperature and liquid nitrogen. They have proven ability to operate up to 1 MHz with a 50 Ω load at 300 K and beyond 10 MHz for loads above 1 kΩ. Simulations suggest that AC-DC difference span less than 30 ppm for frequencies up to 1 MHz for the divider and 200 ppm for the buffer. Although there are some discrepancies between buffer simulation and prototype measurements, the model still possess great explanatory power.

On-chip supercapacitor electrode based on polypyrrole deposited into nanoporous Au scaffold

On-chip supercapacitors hold the potential promise for serving as the energy storage units in integrated circuit system, due to their much higher energy density in comparison with conventional dielectric capacitors, high power density and long-term cycling stability. In this study, nanoporous Au (NP-Au) film on-chip was employed as the electrode scaffold to help increase the electrolyte-accessible area for active material. Pseudo-capacitive polypyrrole (PPY) with high theoretical capacitance was deposited into the NP-Au scaffold, to construct the tailored NP-Au/PPY hybrid on-chip electrode with improved areal capacitance. Half cell test in three- electrode system revealed the improved capacitor performance of nanoporous Au supported PPY electrode, compared to the densely packed PPY nanowire film electrode on planer Au substrate (Au/PPY). The areal capacitance of 37 mF/cm2~10 mV/s, 32 mF/cm2~50 mV/s, 28 mF/cm2~100 mV/s, 16 mF/cm2~500 mV/s, were offered by NP-Au/PPY. Also, the cycling performance was enhanced via using NP-Au scaffold. The developed NP-Au/PPY on-chip electrode demonstrated herein paves a feasible pathway to employ dealloying derived porous metal as the scaffold for improving both the energy density and cycling performance for supercapacitor electrodes.