External Electro-optic Sampling Research Articles

SPECTRO-TEMPORAL MISMATCH ANALYSIS OF A TRANSMISSION LINE BASED ON ON-WAFER OPTICAL SAMPLING

We present an optical sampling technique that enables exploration of mismatches of a microstrip transmission line based on reflection analyses of electromagnetic pulses. The external electro-optic sampling scheme with a minute crystal detects high-speed electrical pulses over arbitrary locations of a line with very low-intrusiveness. The temporal pulsed signals measured with an on-wafer optical probing system and the corresponding spectra are obtained to analyze the transfer characteristics of a microstrip transmission line with 20 GHz bandwidth. The spectro-temporal response was cross-checked with commercial instruments. Applications of this optical probing technique to explore mismatches at the terminal port — based on both time and frequency domain reflectometry analyses — are also presented.

Correction of picosecond voltage pulses measured with external electro-optic sampling tips

We quantify the distortion that an external electro-optic sampling tip imprints on a measured picosecond voltage pulse propagating on a coplanar stripline. In order to characterize the sampling tip, we take advantage of the electro-optic effect of the GaAs substrate onto which the stripline is fabricated. In these measurements, the electro-optic tip just acts as a disturbance of the transmission line. We derive a correction function that allows us to eliminate the influence of the invasive sampling tip on a measured voltage pulse up to a frequency of 400 GHz. The corrected voltage pulse shows good agreement with the true, undisturbed voltage pulse obtained from a sampling measurement using the electro-optic effect of the GaAs substrate. Moreover, the experimental results are supported by finite-difference frequency-domain simulations. Our work paves the way towards a more accurate characterization of high-speed electronic devices using external electro-optic sampling tips.

Characterization of an external electro-optic sampling probe: Influence of probe height on distortion of measured voltage pulses

We experimentally and theoretically investigate the distortion that an external electro-optic sampling tip imprints on a measured voltage pulse that propagates along a coplanar stripline. By using the electro-optic effect of the GaAs substrate on which the stripline is fabricated we obtain the undisturbed voltage pulse, which serves as a reference pulse. This allows us to quantitatively compare the voltage pulse measured with the external electro-optic sampling tip to the undisturbed voltage pulse. The sensitivity of the sampling measurement and the distortion of the voltage pulse are determined for different heights of the tip which is lifted off the stripline. The experimental data agree very well with numerical finite difference calculations. We find that small changes of the tip height already influence the measurements strongly. From the experiments we infer an optimum working height of the sampling tip of only 0.5 μm. Our investigations help to improve the accuracy of electro-optic sampling measurements.

External electro-optic sampling utilizing a poled polymer asymmetric Fabry–Perot cavity as an electro-optical probe tip

External electro-optic sampling utilizing a poled polymer asymmetry Fabry–Perot cavity as electro-optic probe tip has been demonstrated. Electro-optical polymer spin coated on the high-reflectivity mirror (HRM) was corona poled. Thus, an asymmetric F–P cavity was formed based on the different reflectivity of the polymer and HRM and it converted the phase modulation that originates from electro-optic effect of the poled polymer to amplitude modulation, so only one laser beam is needed in this system. The principle of the sampling was analyzed by multiple reflection and index ellipsoid methods. A 1.2 GHz microwave signal propagating on coplanar waveguide transmission line was sampled, and the voltage sensitivity about 0.5 mV/ Hz was obtained.

External Electro-optic Sampling Utilizing an AsymmetricFabry-Pérot Film of Poled Electro-optical Polymer

External electro-optic sampling has been first demonstrated using apoled electro-optical polymer asymmetric Fabry-Pérot film, placed freelyon the indium-tin oxide coplanar waveguide transmission line and used asan electro-optic probe tip. Only one laser beam is required due to the factthat the asymmetric Fabry-Pérot film is utilized to convert the phasemodulation to amplitude modulation. A 1.2 GHz microwave signal issampled, and the voltage sensitivity of about 2 mV/(Hz)1/2 isobtained. The results are promising for technical applications inhigh-speed electronic devices and monolithic microwave integratedcircuits research.

An external electrooptic sampling technique based on the Fabry-Perot effect

Electrooptic sampling has proved itself as the best technique for the measurement of high-speed electronic signals. This is due to its high bandwidth and noninvasiveness. Standard sampling geometries rely on a rotation of polarization within an electrooptic material and subsequent polarization sensitive detection. In this paper, we present results using a simple technique which relies on Fabry-Perot resonances inside the electrooptic material to produce an amplitude modulation. This simplifies the experiment considerably.

Optical second-harmonic probe for ultra-high frequency on-chip interconnects with benzocyclobutene

We report the application of electric field-induced second-harmonic (EFISH) generation for time-resolved measurement of ultra-fast electrical pulses propagating on thin-film microstrip lines fabricated with a polymer based on benzocyclobutene as a dielectric layer on a silicon substrate. This contactless field detection enables the characterization of electric pulses on the transmission line up to 1.95 THz. In comparison to external electro-optic sampling the EFISH technique provides a better characterization tool concerning time-resolution and noninvasiveness.

Electrooptic mapping of near-field distributions in integrated microwave circuits

A field mapping system based on external electrooptic sampling has been developed in order to determine the vectorial components of the electric near-field distribution within microwave integrated circuits. The capabilities of the setup are demonstrated by two-dimensional measurements of normal and tangential fields in a coplanar microwave distribution network at frequencies up to 15 GHz. Results obtained on a functioning power-distribution network, as well as on two nonfunctioning networks, show the ability of the technique to interrogate internal circuit operation and to isolate faults through investigation of the field distributions.

Electro-optic near-field mapping of planar resonators

A comprehensive experimental and theoretical study for the determination of the electric near-field above planar resonators is presented. The transverse component of the electric field is mapped by external electro-optic (EO) sampling technique with high spatial and temporal resolution. The evolution of the near-field radiation pattern of the investigated 7-GHz planar resonator to the onset of the far-field pattern is traced by measurements at various heights above the sample. Frequency-dependent measurements allow to characterize the field pattern changes when the frequency is swept through the main resonance. Additional undesired resonances are identified by the detected mode pattern. The experimental data are reproduced by simulations based upon an electric field integral equation (EFIE) method.

Fabry-Pérot enhancement of external electro-optic sampling

This paper describes the Fabry-Perot enhancement of external electro-optic sampling. Previous reports of Fabry-Perot enhancement have been exclusively on continuous wave systems. Using a picosecond dye laser and a standard electro-optic probe tip an increase is shown both in the sensitivity and the responsivity of the picosecond probing system. The results show that for a picosecond system considerable advantage can be gained by use of the Fabry-Perot effect.

Optoelectronic techniques for ultrafast device network analysis to 700 GHz

Recent advances in state-of-the-art optoelectronic techniques are presented for small-signal electronic device network analysis. The impetus for optoelectronic approaches is given by the severely inadequate bandwidth coverage of existing measurement techniques. Based on a comparison of the trade-offs offered by various optoelectronic techniques, external electrooptic sampling was chosen. Then, the three basic building blocks of an electrooptic characterization system are discussed, which cover the areas of wide-band signal measurement, generation and transmission. The building blocks are subsequently integrated into a complete electrooptic network analyser system capable of active device characterization over a 100 GHz bandwidth. These capabilities are demonstrated on a heterojunction field-effect transistor with a directly-measured maximum frequency of oscillation of 94 GHz. Then, the performance of the electrooptic network analyser is optimized by minimizing transmission line losses, and by improving signal generation and measurement geometries. The resulting system exhibits an unprecedented single-measurement bandwidth of 700 GHz on passive structures. The system performance is verified by comparing measured results with simple models of the measured passive structures.

Heterobarrier photodiode MSM structures with subpicosecond temporal resolution

Interdigital heterobarrier metal—semiconductor—metal (MSM) structures are proposed as ultrafast photodetectors of visible radiation. Vertical photocarrier drift in MSM diode structures provides the simplest way of reducing the active region of a detector to a submicron size and of considerably shortening the response time without a significant loss of the radiation coupling efficiency. External electrooptic sampling was used to determine the subpicosecond (half-amplitude duration 0.6 ps) electrical response of a detector built into a coplanar microwave transmission line. Under a bias voltage of 1 V and for an optical excitation energy of 10 pJ per pulse the change in the photodiode voltage amounted to 40% of the bias voltage, which makes these diode structures sufficiently efficient and extremely fast detectors of optical radiation.

Coplanar transmission lines on thin substrates for high-speed low-loss propagation

We investigate the attenuation and phase velocity characteristics of coplanar strip (CPS) transmission lines designed for high-speed, low-loss propagation at sub-THz frequencies. Photoconductor switches driven by femtosecond optical pulses were used to generate propagating picosecond electrical transients. External electrooptic sampling was used to measure the time-domain impulse-response characteristics with subpicosecond time resolution. The finite-difference transmission-line-matrix (FD-TLM) numerical method was used to model picosecond pulse propagation on identical transmission lines. The experiment and the numeric simulations have clarified nonquasistatic high-frequency effects and were shown to agree over a 500 GHz frequency range. Additionally, analytic quasi-static velocity and characteristic impedance formulas have been verified and their frequency range of validity established for the investigated CPS geometries. Radiation into the substrate is the dominant loss mechanism at frequencies above /spl sim/100 GHz for the CPS lines on thick substrates. CPS transmission line fabrication on thin substrates has been proposed as a method for reducing high-frequency loss and increasing the microwave propagation velocity. CPS transmission lines fabricated on 8-/spl mu/m-thick Si membranes have been studied and demonstrated to possess the desired high-speed, low-loss properties.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The role of internal waveform measurements in IC development

It will be argued that when internal waveform measurements become a standard procedure in IC development, both development time and IC quality will benefit. To achieve this, the following technical problems have to be solved: electrical interfacing, choice of measuring method, sample preparation and determination of measuring strategy. These items will be examined and some case studies involving external electro-optic sampling and needle probing will be presented.

An automated electro-optic probing system for ultra-high-speed IC's

This paper describes an automated optical probing system based on external electro-optic sampling for the internal diagnoses of ultra-high-speed IC's. A workstation-controlled environment, automatic probe positioner, and module-based system architecture make the system easy to use, and improve measurement accuracy and reproducibility. Voltage sensitivity is routinely obtained on an order of 1 mV//spl radic/(Hz) at frequencies up to 70 GHz. The system has been successfully applied to the internal-node measurement of on-wafer digital IC's operating at 20 Gb/s.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Invasiveness of LiTaO/sub 3/ and GaAs probes in external E-O sampling

Disturbances of signals on a coplanar waveguide (CPW) induced by the presence of LiTaO/sub 3/ and GaAs electrooptic probes in external electrooptic (EO) sampling have been simulated and compared quantitatively. The finite-difference-time-domain method is used to simulate the full wave field around a coplanar waveguide on a GaAs substrate in an external EO sampling configuration. The results indicate that the induced signal disturbance, or invasiveness, of a LiTaO/sub 3/ probe is almost ten times that of a GaAs probe in terms of the magnitude of S/sub 11/, but that LiTaO/sub 3/ yields about two times the EO response for a given S/sub 11/ and optical probing wavelength. The transparency of LiTaO/sub 3/ to shorter wavelengths, however, allows an even higher sensitivity for this material relative to GaAs. The results suggest that these probes do not exhibit significant invasiveness (magnitude of S/sub 11/ smaller than -40 dB), if they are removed from contact by the distance of CPWs center conductor width.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ultrahigh-bandwidth vector network analyzer based on external electro-optic sampling

We report the development of an ultrahigh-bandwidth vector network analyzer useful for small-signal characterization of high-speed semiconductor devices. It employs 100-fs optical pulses for making terahertz-bandwidth electro-optic measurements of electrical signals, as well as for sub-picosecond, photoconductive, electrical-stimulus-signal generation. High-bandwidth coplanar strip transmission lines are used for signal transmission. A 0.15 × 50 μm gate AlGaAs/InGaAs/GaAs HFET has been characterized over a bandwidth of 100 GHz using this network analyzer. A comparison with conventional RF network analyzer measurements performed to 40 GHz demonstrated good agreement throughout this bandwidth. Such measurements of the actual device characteristics across their entire operating frequency range should improve device development and incorporation into active circuits.

Electron beam testing versus laser beam testing

After a short discussion of trends in microelectronics, an overview of modern contactless internal probing techniques is given. Two techniques, electron beam testing and electro-optic sampling, are selected for comparison from the standpoint of the main application, namely CMOS technology. Basic principles are summarized and spatial, temporal and voltage resolution are discussed together with some practical aspects. Electron beam testing has a superior spatial resolution of 0.1 μm or better, while external electro-optic sampling can achieve better temporal resolution below 1 ps. Although the voltage sensitivity of the latter can be significantly better, a real quantitative measurement of internal signals has not yet been attained, whereas the former enables exact voltage measurements even at submicron lines. As a practical example, internal measurements at a 7 GHz divider with both probing techniques are compared.

Terahertz attenuation and dispersion characteristics of coplanar transmission lines

Experimental verification of analytic formulas for the dispersion and the attenuation of electrical transient signals propagating on coplanar transmission lines is presented. The verification is done in the frequency domain over a terahertz range although the experiments are in the time domain. The analytic formulas are obtained from fits to the full-wave analysis results. It is quantitatively verified that the full-wave steady-state solutions can be directly applied to the transient time-domain propagation experiments. Subpicosecond electrical pulses and an external electrooptic sampling technique are used to obtain the time-domain propagation data. From the Fourier transforms of the time-domain data both the attenuation and the phase information as a function of frequency are extracted. The dispersion and the attenuation characteristics are investigated for both coplanar waveguide and coplanar strip transmission lines. The investigation is carried out on both semiinsulating semiconductor and dielectric substrate materials. No observable losses caused by the semiconductor material are indicated. >

Picosecond electro-optic probing of high-speed integrated circuits using external GaAs tip

External electro-optic sampling has been demonstrated on high-speed integrated circuits using a pulse-compressed mode-locked Nd : YAG laser and a sophisticated GaAs probe tip. The measurement at frequencies up to 40 GHz has been successfully performed with excellent voltage sensitivity of less than 3 mV/√(Hz).