Badri Tiwari

Thermal infrared detection using dipole antenna-coupled metal-oxide-metal diodes

This work focuses on dipole antenna-coupled metal-oxide-metal diodes, which can be used for the detection of long wave infrared radiation. These detectors are defined using electron beam lithography and fabricated with shadow evaporation metal deposition. Along with offering complementary metal oxide semiconductor compatible fabrication, these detectors promise high speed and frequency selective detection without biasing, a small pixel footprint, and full functionality at room temperature without cooling. Direct current current-voltage characteristics are presented along with detector response to 10.6μm radiation. The detection characteristics can be tailored to provide for multispectral imaging in specific applications by modifying device geometries.

Controlled etching and regrowth of tunnel oxide for antenna-coupled metal-oxide-metal diodes

The authors have designed a new procedure for fabrication of infrared (IR) sensors. These sensors consist of a dipole antenna coupled with a metal-oxide-metal (MOM) (Al–AlOx–Pt) diode. The surface of electron beam evaporated Al, serving as one of the electrodes, is cleaned using an Ar plasma, followed by in situ controlled growth of the tunneling oxide, AlOx. The antenna, its leads, and the overlap of the Al and Pt electrodes that defines the MOM overlap area are all defined using electron beam lithography. The MOM overlap area of these devices is as small as 50×80 nm2. Features of our process include the use of dissimilar metals for the formation of the MOM diode, small MOM diode size, and controlled etching and regrowth of the tunneling oxide. A CO2 laser at 10.6 μm was used for the IR characterization of these sensors. Current-voltage and IR measurements are presented. The normalized detectivity (D∗) for these devices was found to be 2.13×106 cm Hz1/2 W−1.

Response Increase of IR Antenna-Coupled Thermocouple Using Impedance Matching

The response of a bowtie antenna-coupled thermocouple operating at 10.6 μm is studied for varying lengths of a transmission line, which connects the antenna to the thermocouple and functions as an impedance-matching element. Peaks in the response are observed for several lengths of transmission line. Most notably, the response of a device with a transmission line length of 1.3 μm is increased 2.4 fold when compared to the device without the transmission line. The analytical response of a microwave circuit describing the detector is in agreement with the measurements, indicating that the increases in the response are caused by an improved impedance match between the antenna and thermocouple facilitated by the transmission line. This experiment demonstrates for the first time impedance matching principles applied to infrared antenna-coupled thermal detectors.

Nano Antenna Array for Terahertz Detection

Infrared (IR) detectors have been fabricated consisting of antenna-coupled metal-oxide-metal diodes (ACMOMDs). These detectors were defined using electron beam lithography with shadow evaporation metal deposition. They are designed to be sensitive to the IR range and work at room temperature without cooling or biasing. In order to achieve large arrays of ACMOMDs, nanotransfer printing have been used to cover a large area with metal-oxide-metal (MOM) diodes and with antenna structures. The printed antenna structures consist of gold and aluminum and exhibit a low electrical resistivity. A large area array of MOM tunneling diodes with an ultrathin dielectric ( ~ 3.6-nm aluminum oxide) has also been fabricated via the transfer-printing process. The MOM diodes exhibit excellent tunneling characteristics. Both direct and Fowler-Nordheim tunneling has been observed over eight orders of magnitude in current density. Static device parameters have been extracted via kinetic Monte Carlo simulations and have confirmed the existence of a dipole layer at the aluminum/aluminum oxide interface of the printed tunneling diodes. The mechanical yield of the transfer-printing process for the MOM tunneling diodes is almost a 100%, confirming that transfer printing is suitable for large area effective fabrication of these quantum devices.

Rectennas Revisited

In the late 1960s, a new concept was proposed for an infrared absorbing device called a “rectenna” that, combining an antenna and a nanoscale metal-insulator-metal diode rectifier, collects electromagnetic radiation in the terahertz regime, with applications as detectors and energy harvesters. Previous theories hold that the diode rectifies the induced terahertz currents. Our results, however, demonstrate that the Seebeck thermal effect is the actual dominant rectifying mechanism. This new realization that the underlying mechanism is thermal-based, rather than tunneling-based, can open the way to important new developments in the field, since the fabrication process of rectennas based on the Seebeck effect is far simpler than existing processes that require delicate tunnel junctions. We demonstrate for the first time the fabrication of a rectenna array using an efficient parallel transfer printing process featuring nearly one million elements.

Nanoantenna Infrared Detectors

This project focuses on devices that can be used for detection of thermal or long-wave infrared radiation, which is a frequency range for which developing detectors is of special interest. Objects near 300 K, such as humans and animals, emit radiation most strongly in this range, and absorption is relatively low in the LWIR atmospheric window between 8 and 14 μm. These facts provide motivation to develop detectors for use in this frequency range that could be used for target detection, tracking, and navigation in autonomous vehicles. The devices discussed in this chapter, referred to as dipole antenna-coupled metal-oxide-metal diodes (ACMOMDs), feature a half-wavelength antenna that couples electromagnetic radiation to a metal-oxide-metal (MOM) diode, which acts as a nonlinear junction to rectify the signal. These detectors are patterned using electron beam lithography and fabricated with shadow evaporation metal deposition. Along with offering CMOS compatible fabrication, these detectors provide high-speed and frequency-selective detection without biasing, a small pixel footprint, and full functionality at room temperature without cooling. The detection characteristics can be tailored to provide for multi-spectral imaging in specific applications by modifying device geometries. This chapter gives a brief introduction to currently available infrared detectors, thereby providing a motivation for why ACMOMDs were chosen for this project. An overview of the metal-oxide metal diode is provided, detailing principles of operation and detection. The fabrication of ACMOMDs is described in detail, from bonding pad through device processes. Direct-current current–voltage characteristics of symmetrical and asymmetrical antenna diodes are presented. An experimental infrared test bench used for determining the detection characteristics of these detectors is detailed, along with the figures of merit which have been measured and calculated. The measured performance of fabricated ACMOMDs is presented, including responsivity, noise performance, signal-to-noise ratio, noise-equivalent power, and normalized detectivity. The response as a function of infrared input power, polarization dependence, and antenna-length dependence of these devices is also presented.

Nanostructure antennas for the LW-IR regime

We review our previous work demonstrating planar dipole antenna structures which operate in the LW-IR regime (30 THz). Integrated metal-oxide-metal tunnel diodes are used as the rectifying element. These nanoantenna structures exhibit a polarization and length dependence expected from classical dipole antennas. We measure specific detectivities of 2*106 cmHz½W−1. One way of increasing the detectivity of these antenna structures, which currently are fabricated on top of a silicon-silicon dioxide structure, is to place them on top of a cavity filled with a low-k dielectric to achieve higher antenna gain. We have explored the performance of cavity-backed dipoles for LW-IR operation by numerical simulations, and have experimentally verified the performance of these structures with a 1000-x scale model operating in Ka-band (30 GHz).

Investigation of the Infrared Radiation Detection Mechanism for Antenna-Coupled Metal-(Oxide)-Metal Structures

At room temperature (300 K), the electromagnetic (EM) radiation emitted by humans and other living beings peaks mostly in the long-wavelength infrared (LWIR) regime. And since the atmosphere shows relatively little absorption in this EM band, applications such as target detection, tracking, active homing, and navigation in autonomous vehicles extensively use the LWIR frequency range. Antennas are scalable, frequency selective, and polarization sensitive and hence present themselves as good candidate for such detectors. The research work presented in this chapter is focused on developing an antenna-based, uncooled, and unbiased detector for the LWIR regime.

Long-wave infrared detection using dipole antenna-coupled metal-oxide-metal diodes

Summary form only given. The integration of nanoelectronic sensor devices with silicon CMOS devices is an important avenue in nanoelectronics. There are countless nanoelectronic devices currently being explored, but they must be integrated with current technologies in order to be utilized in the near future. In this paper, we report on infrared sensors that are compatible with CMOS technology, and thus can readily be implemented with CMOS circuitry.