Richard Hopper

A highly efficient CMOS nanoplasmonic crystal enhanced slow-wave thermal emitter improves infrared gas-sensing devices

The application of plasmonics to thermal emitters is generally assisted by absorptive losses in the metal because Kirchhoff’s law prescribes that only good absorbers make good thermal emitters. Based on a designed plasmonic crystal and exploiting a slow-wave lattice resonance and spontaneous thermal plasmon emission, we engineer a tungsten-based thermal emitter, fabricated in an industrial CMOS process, and demonstrate its markedly improved practical use in a prototype non-dispersive infrared (NDIR) gas-sensing device. We show that the emission intensity of the thermal emitter at the CO2 absorption wavelength is enhanced almost 4-fold compared to a standard non-plasmonic emitter, which enables a proportionate increase in the signal-to-noise ratio of the CO2 gas sensor.

A Low-Power, Low-Cost Infra-Red Emitter in CMOS Technology

In this paper, we present the design and characterization of a low-power low-cost infra-red emitter based on a tungsten micro-hotplate fabricated in a commercial 1-μm silicon on insulator-CMOS technology. The device has a 250-μm diameter resistive heater inside a 600-μm diameter thin dielectric membrane. We first present electro-thermal and optical device characterization, long term stability measurements, and then demonstrate its application as a gas sensor for a domestic boiler. The emitter has a dc power consumption of only 70 mW, a total emission of 0.8 mW across the 2.5-15-μm wavelength range, a 50% frequency modulation depth of 70 Hz, and excellent reproducibility from device-to-device. We also compare two larger emitters (heater size of 600 and 1800 μm) made in the same technology that have a much higher infra-red emission, but at the detriment of higher power consumption. Finally, we demonstrate that carbon nanotubes can be used to significantly enhance the thermo-optical transduction efficiency of the emitter.

Micro-Raman/Infrared Temperature Monitoring of Gunn Diodes

Temperature measurements have been made on Gunn diode samples, using both infrared (IR) and micro-Raman spectroscopy. Micro-Raman spectroscopy was used to give high-resolution temperature measurements on the active transit region of the Gunn diode. These were directly compared with IR thermal measurements made across the mesa region and also on the metallized top contact of the diode.

Reduction of Impact Ionization in GaAs-Based Planar Gunn Diodes by Anode Contact Design

Impact ionization in GaAs-based planar Gunn diodes is studied through electroluminescence (EL) analysis with the aim of reducing its magnitude by means of contact design and shaping, and thus enhance device performance and reliability. Designs in which the diode ohmic anode has an overhanging Schottky extension (composite anode contact) are shown to result in a significantly reduced amount of impact ionization, as compared with a simple ohmic contact design. The EL results are consistent with Monte Carlo simulations, which show a reduced impact ionization in composite anode contact devices due to a reduced electron density beneath the anode Schottky extension that, on the one hand, weakens the Gunn domain electric field and softens its variations near the anode edge, and, on the other hand, reduces the number of electrons capable of generating holes by impact ionization. A comparison between standard and composite anode contact approaches in terms of radio-frequency operation of the devices is made showing oscillations up to 109 GHz with an output power of -5 dBm in devices featuring the composite anode contact and no oscillations from all-ohmic contact devices. The findings reported in this paper may be useful not only for the design and the fabrication of planar Gunn diodes but also for other devices such as high-electron-mobility transistors where impact ionization can result in reliability limitations.

Improved infrared (IR) microscope measurements for the micro-electronics industry

Infrared (IR) measurements of the surface temperature of electronic devices have improved over the last decade. However, to obtain more accurate surface temperatures the devices are often coated with a high emissivity coating leading to temperature averaging across the device surface and damage to the device. This paper will look at the problems of making accurate surface temperature measurements particularly on areas of semiconductor and will address the surface emissivity correction problem using novel measurement approaches.