http://www.ultra-project.eu/
THz instruments:
As illustrated by the citation above from a Phys. Rev. publication by Rubens and Nichols in 1897, there is a longstanding effort to close the breach in the electromagnetic spectrum between microwaves and optics. The THz frequency range is defined as the band of the electromagnetic spectrum extending from roughly 0.1 THz to 10 THz, depending on the definition, i.e. between the microwave and the infrared range. The techniques normally used in microwaves and optics are not useful to access this band. Although some means to reach the THz range and strong interest in the field have been present for more than 50 years, given the wide range of possible applications [1,2]. However, the fact that even nowadays State-of-the-Art systems to generate and process THz radiation are still bulky, discrete and power hungry has drastically limited the range of possible applications.
The situation has slowly changed in the last years since the invention of the THz Time Domain Spectroscopy (THz-TDS) techniques in the early 90’s [3] which has allowed the first use of this radiation and even the introduction of first commercial products. It is clear, however, that further simplification of THz systems would open a whole new set of scientific and business opportunities.
Present systems are based on using ultrashort femtosecond laser systems in combination with adequate optoelectronic transducers [3] to generate THz radiation. One widely used optoelectronic transducer is illustrated to the right, showing a photoconductive structure embedded into an antenna to generate and sample THz radiation at the time point such a structure is activated by a femtosecond laser pulse. Such components lead to powerfull THz systems in a typical correlated sampling type of approach, where THz pulses are generated and detected with femtosecond laser pulses and the correlation of generation and detection time points leads to a time-resolved detection of the THz properties. An exemplary system is illustrated below. Such systems have advantageous properties (bandwidth 100GHz up to 120THz , noise floor 6·10-16 W / Hz1/2, resolution up to 90dB). However, such systems still rely on costly femtosecond laser systems and typical systems are therefore too bulky and costly to allow a widespread application.
The goal of the ULTRA project is to develop cost efficient compact fully-electronic THz technologies, preferentially realized in a fully CMOS compatible process. Two electronic integrated lab-on-chip THz instruments for use in medical and chemical/biological analysis and tissue identification will be developed.
References:
The situation has slowly changed in the last years since the invention of the THz Time Domain Spectroscopy (THz-TDS) techniques in the early 90’s [3] which has allowed the first use of this radiation and even the introduction of first commercial products. It is clear, however, that further simplification of THz systems would open a whole new set of scientific and business opportunities.
Present systems are based on using ultrashort femtosecond laser systems in combination with adequate optoelectronic transducers [3] to generate THz radiation. One widely used optoelectronic transducer is illustrated to the right, showing a photoconductive structure embedded into an antenna to generate and sample THz radiation at the time point such a structure is activated by a femtosecond laser pulse. Such components lead to powerfull THz systems in a typical correlated sampling type of approach, where THz pulses are generated and detected with femtosecond laser pulses and the correlation of generation and detection time points leads to a time-resolved detection of the THz properties. An exemplary system is illustrated below. Such systems have advantageous properties (bandwidth 100GHz up to 120THz , noise floor 6·10-16 W / Hz1/2, resolution up to 90dB). However, such systems still rely on costly femtosecond laser systems and typical systems are therefore too bulky and costly to allow a widespread application.The goal of the ULTRA project is to develop cost efficient compact fully-electronic THz technologies, preferentially realized in a fully CMOS compatible process. Two electronic integrated lab-on-chip THz instruments for use in medical and chemical/biological analysis and tissue identification will be developed.
References:
- P.H. Siegel, “Terahertz Technology in Biology and Medicine”, IEEE Trans. On Microwave Theory and Tech. 52, NO. 10, October 2004.
- P. de Maagt, P. Haring Bolivar and C. Mann, Terahertz science, engineering and systems—from space to earth applications, Encyclopedia of RF and Microwave Engineering, Ed. by K. Chang, pp. 5175-5194 (John Wiley & Sons, Inc., 2005) ISBN 0-471-27053-9.
- B.B. Hu and M.C. Nuss, “Imaging with terahertz waves”, Opt. Lett. vol. 20, pp. 1716-1718, 1995
The goal of the ULTRA project is the development of THz systems for medical, biological and chemical analysis. The combination of electronic, microfluidic, THz and 3D packaging technologies will enable low-cost, reliable and highly-integrated solutions for these emerging markets.
THz IC Design
The aim of the ULTRA project is to build two integrated THz imagers / spectrometers in the form of demonstrators. In order to achieve this objective a robust, integrated and efficient source of THz radiation must be used along with a suitable detection mechanism. The ULTRA consortium suggests the use of nonlinear transmission lines (NLTLs) as essential components to generate pico-second wide (hence THz) electrical signals to be used in the transmitter and the receiver part of the system.
NLTLs are sections of linear transmission lines loaded with nonlinear (i.e. voltage dependant) capacitances and are used to compress a broad input pulse into a narrow pulse with a broadband spectral content up to 1THz or more. Spectrometers based on NLTLs have been already studied [1][2][3] and are shown to be working well, but although they exploit integrated NLTLs on Gallium Arsenide, they still use a large number of external bulky components. In the ULTRA project the target is to integrate all the necessary components on a single board, shrinking down the size and the power consumption. The consortium will investigate the possibility to integrate all the necessary components on a 65nm CMOS chip. Attempts to use CMOS devices have been successfully carried out, but are usually limited to 0.18mm BiCMOS [4] or 0.18mm CMOS [5] technologies and are limited to the study of the NLTL block. A fully integrated lab-on-chip or lab-in-package THz spectrometer such as the one targeted by ULTRA (i.e. without any non-integrable external components as a femto-second laser) is not even mentioned, for the moment, in the open literature.
NLTLs are sections of linear transmission lines loaded with nonlinear (i.e. voltage dependant) capacitances and are used to compress a broad input pulse into a narrow pulse with a broadband spectral content up to 1THz or more. Spectrometers based on NLTLs have been already studied [1][2][3] and are shown to be working well, but although they exploit integrated NLTLs on Gallium Arsenide, they still use a large number of external bulky components. In the ULTRA project the target is to integrate all the necessary components on a single board, shrinking down the size and the power consumption. The consortium will investigate the possibility to integrate all the necessary components on a 65nm CMOS chip. Attempts to use CMOS devices have been successfully carried out, but are usually limited to 0.18mm BiCMOS [4] or 0.18mm CMOS [5] technologies and are limited to the study of the NLTL block. A fully integrated lab-on-chip or lab-in-package THz spectrometer such as the one targeted by ULTRA (i.e. without any non-integrable external components as a femto-second laser) is not even mentioned, for the moment, in the open literature.
- Y. Konishi et al., “Picosecond electrical spectroscopy using monolithic GaAs circuits”, Appl. Phys. Lett. 61 (23), Dec. 1992
- D.W. van der Weide et al., “All-electronic generation of 880 fs, 3.5V shockwaves and their application to a 3 THz free-space signal generation system”, Appl. Phys. Lett. 62 (1), Jan 1993
- J.S. Bostak et al., “All-electronic terahertz spectroscopy system with terahertz free-space pulses,” J. Opt. Soc. Am. B 11, No. 12, 2561-2565 (1994).
- E. Afshari and A. Hajimiri, “Nonlinear Transmission Lines for Pulse Shaping in Silicon”, IEEE J. of Solid-State Cir., vol. 40, no. 3, March 2005
- D.S Ricketts et al., “Electrical Soliton Oscillator”, IEEE Trans. Microw. Theory Tech., vol. 54, no. 1, Jan. 2006
Plasmonics:
Plasmonics or surface plasmon polariton optics is a recent development of electromagnetism dealing with the control of the propagation of surface plasmon polaritons (SPPs). SPPs are electromagnetic waves coupled to charge carriers at the interface between a dielectric and a conductor. This coupling leads to a strong confinement of the electromagnetic energy to the interface, characterized by an evanescent decay of the field amplitude away from the surface. SPPs can propagate along the surface with a propagation length determined by the ohmic losses in the conductor, by absorption in the dielectric and by scattering with inhomogeneities on the surface. This scattering can be also controlled and used to modify the propagation of SPPs in a similar manner as it is done with mirrors, lenses and waveguides with free space electromagnetic radiation. Scientists have started using plasmonics in the optical and infrared range for biosensing applications essentially because the enhanced electromagnetic field of the SPPs at the surface gives unprecedented sensitivity and also allows label-free detection. However, the very large permittivity of metals at THz frequencies leads to a weak coupling between the electromagnetic field and the free charge carriers. In this case SPPs are referred to as Zenneck waves and they are loosely bound to the surface, resembling an electromagnetic wave propagating grazing to the surface. In the case of a gold-air interface the decay of a Zenneck wave into air at 1 THz is as large as 5 cm. Doped semiconductors have a much lower permittivity than metals at THz frequencies, leading to strongly coupled SPPs to semiconductor-dielectric interfaces. The decay length of THz SPPs on semiconductor surfaces is on the order of a few hundred micrometers. An alternative to semiconductors for efficient THz plasmonics are metallic surfaces perforated with arrays of holes much smaller than the wavelength of the THz radiation. These structures have a larger effective skin depth or penetration of the field into the effective medium defined by the structured metal leading to a surface mode that mimics a SPP on a flat surface.
One of the aims of the ULTRA project is to use THz radiation instead of infrared or visible light for selective detection of tissues and other materials by exploiting the peculiar spectral signatures of these materials in the THz frequency range. In order to increase the sensitivity we plan to use THz SPPs as a probe. Terahertz SPPs will increase the sensitivity for detection by a factor proportional to the electromagnetic field enhancement at the surface which in optimized structures can be of several orders of magnitude. This increased sensitivity will have a large impact on the realization of accurate and reliable analysis using small amounts of chemical and biological agents.
One of the aims of the ULTRA project is to use THz radiation instead of infrared or visible light for selective detection of tissues and other materials by exploiting the peculiar spectral signatures of these materials in the THz frequency range. In order to increase the sensitivity we plan to use THz SPPs as a probe. Terahertz SPPs will increase the sensitivity for detection by a factor proportional to the electromagnetic field enhancement at the surface which in optimized structures can be of several orders of magnitude. This increased sensitivity will have a large impact on the realization of accurate and reliable analysis using small amounts of chemical and biological agents.
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