Electro-optic Sampling System for on Wafer Characterization of Ultra Fast Electronics

Systems with ultra high spectral bandwidth up to THz frequencies are applicable in many fields of science and technology. Recently fully electronic systems are being developed as a key technology to enable a widespread use of THz technologies. Compared to laser based THz systems which are extremely expensive and bulky; electronic THz systems can be realized in a low cost, low power consumption and very compact form.

Despite a significant technological development, such electronic systems can hardly be characterized. In order to analyze the function of such ultra fast electronic circuit, conventional instruments like Network Analyzers can only measure in range of a few hundreds of GHz, which does not cover the full frequency range of modern electronic devices. In the Ultra project we are building up an electro-optic sampling system capable to measure and characterize electronic components, circuits and systems up to the THz frequency range. The main features of this system are:

  • Detection of the amplitude and phase of internal signals with an ultrahigh bandwidth beyond 1 THz.
  • Freely probing of electric signals over the device under test (not only at dedicated ports).
  • Direct on-wafer characterization that reduces the cost and time of circuits test.
  • Scanning capabilities to derive electric field maps on a circuit to detect malfunctions or to derive circuit synchronization problems.

Terahertz Time Domain Spectroscopy Reflectivity Setup for Biomolecular Sensing in Aqueous Solutions

Some efforts have been recently made in order to progressively attack one of the big remaining practically unsolved problems that is employing THz radiation for biomolecular sensing in aqueous solutions. Measurements in diluted environments are clearly limited due to extremely high and also temperature depending absorption coefficients of water in the far infrared range between 0.2 and 10 THz.

A multitude of biomolecules e.g. amino acids, peptides, carbohydrates and DNA has been thoroughly investigated with regard to THz induced low frequency intra- and intermolecular vibrational and rotational modes in dried samples or partially hydrated powders. In fact, real application-oriented future generations of THz biosensors will be undoubtful focusing on biomolecular studies of aqueous samples, containing rather small solute concentrations enclosed in highly complex liquid matrices. Taking into account solvation dynamics and hydration effects of biomolecules, protein structure information and folding kinetics may be accessible as well. Mainly, two possible ways of THz sensing in aqueous media have been already discussed in literature. Both show either the potential to derive spectroscopic peak information (ATR) in the lower THz frequency range or different absorption coefficients from recorded amplitude and phase information of the THz TDS signal according to different biomolecular concentrations in aqueous samples. Against this background, one fundamental demand involves the conservation of biomolecular natural conformational states in order to retain protein functionalities, activities of catalytic sites or interactions of surface sites presented to the molecule surrounding water shells.

Considering typical characteristics of applicable, low cost and highly integrated biosensors i.e. maximum selectivity, supreme sensitivity, appropriate for daily use, long time stability, reproducibility and robustness combined to a minimum number of sample preparation steps, actually there clearly still is the challenge to discover and present new approaches enabling THz based biomolecular sensing principles. Whose potential must considerably exceed beyond the stage of demonstrating proof-of-principle measurements.

The main feature of the THz TDS reflectivity setup investigated in our labs includes potentially high sensitivity THz biomolecular sensing in aqueous solutions concurrently circumventing the hitherto existing sensing limits of biomolecule detection in very thin water layers in the lower µm range.