Marko Obradov

Temperature measurement using silicon piezoresistive MEMS pressure sensors

In industrial processes, as well as in many other fields from vehicles to healthcare, temperature and pressure are the most common parameters to be measured and monitored. Silicon microelectromechanical (MEMS) piezoresistive pressure sensors are the first and the most successful MEMS sensors, widely used in the industry in various measurement configurations. The inherent temperature dependence of the output signal of such sensors adversely affects their pressure measurement performance. However, it can be utilized for temperature measurement, thus enabling new sensor applications. In this paper a method is presented for temperature measurement using MEMS piezoresistive pressure sensors.

Suppression of noise in semiconductor infrared detectors using plasmonics

We consider the enhancement of the specific detectivity of semiconductor infrared photodetectors for the mid-infrared range utilizing spherical submicrometer plasmonic particles with redshifted spectral characteristics. The optical field is strongly concentrated near the plasmonic particle located on top of the detector active area; thus, the necessary thickness of the device is significantly reduced. In order to ensure the plasmonic effect in infrared, we apply a redshifting strategy based on the simultaneous use of doped transparent conductive oxides (TCO) with a lower plasma frequency compared to metals and an embedding high-permittivity dielectric that further redshifts the spectral characteristics. A graded antireflective layer with a linear increase of the refractive index is applied on top of the structure. We perform ab initio simulation of the optical response of the whole system utilizing the finite element method. As an illustrative example, we analyze a mercury cadmium telluride infrared detector with an epitaxial active layer. We observe suppression of the overall generation-recombination (g-r) noise level (Auger, radiative and Shockley?Read) due to the decrease of the volume of the active region. The specific detectivity of the system is simultaneously increased by optical field localization (light management) and by noise suppression. An elevation of the operating temperature of the detector is observed as a result. According to our simulations, a specific detectivity enhancement of more than an order of magnitude should be readily achievable.

A low-loss double-fishnet metamaterial based on transparent conductive oxide

In this work, we consider the applicability of transparent conductive oxide (TCO) materials such as indium tin oxide (ITO) for the fabrication of fishnet metamaterials. We utilized the finite element method to simulate the scattering parameters of the ITO-based fishnet metamaterial with rectangular aperture in a 300 nm-square unit cell. We further used effective extraction methods to retrieve the complex effective refractive index and the impedance of the metamaterial. We calculated the figure of merit defined as the ratio between the real and the imaginary parts of the effective dielectric permittivity of the ITO-based double-fishnet metamaterial and compared it with that of gold-based fishnets. We conclude that the use of TCO can decrease overall losses in fishnet metamaterial and increase the figure of merit. Our approach does not require the use of active media with external pumping and at the same time is applicable to any metamaterial geometry.

A method enabling simultaneous pressure and temperature measurement using a single piezoresistive MEMS pressure sensor

In this paper we present a high-performance, simple and low-cost method for simultaneous measurement of pressure and temperature using a single piezoresistive MEMS pressure sensor. The proposed measurement method utilizes the parasitic temperature sensitivity of the sensing element for both pressure measurement correction and temperature measurement. A parametric mathematical model of the sensor was established and its parameters were calculated using the obtained characterization data. Based on the model, a real-time sensor correction for both pressure and temperature measurements was implemented in a target measurement system. The proposed method was verified experimentally on a group of typical industrial-grade piezoresistive sensors. The obtained results indicate that the method enables the pressure measurement performance to exceed that of typical digital industrial pressure transmitters, achieving at the same time the temperature measurement performance comparable to industrial-grade platinum resistance temperature sensors. The presented work is directly applicable in industrial instrumentation, where it can add temperature measurement capability to the existing pressure measurement instruments, requiring little or no additional hardware, and without adverse effects on pressure measurement performance.

Plasmonic metamaterial with fishnet superlattice for enhanced chemical sensing

In this work we consider a novel type of superlattice fishnet metamaterial for chemical sensing. By superimposing two fishnet metamaterial lattices we aim to achieve increased functionality compared to the standard fishnet metamaterials. We investigate spectral response of our structure to the changes in surrounding medium to be utilized in single wavelength readout chemical sensing. Additionally we compare the dispersion relation of plasmon modes in our superlattice fishnet metamaterial to the single lattice metamaterial and analyze the nature of coupling between plasmon modes. We present possibilities for multispectral sensing operation as well as for switching the resonant plasmon modes between sublattices by purely optical means.

Redshifting approach for nanoplasmonic enhancement of semiconductor infrared detectors

In this work we consider the enhancement of ultimate performance of semiconductor infrared detectors utilizing nanoplasmonics. To this purpose we analyze the application of transparent conductive oxides (TCO) as plasmonic material with the plasma frequency in the near infrared. We investigate the possibility to apply TCO nanoparticles for field localization embedded into a dielectric host. We consider a further redshift by methods originally proposed for solar cell in the UV and visible part of the spectrum. One such method is the use of a high refractive index for the host dielectric. We base our considerations on our thin-film uncooled mercury cadmium telluride (HgCdTe) photoconductive detectors.