Toshihiko Kiwa

Laser terahertz-emission microscope for inspecting electrical faults in integrated circuits

A laser terahertz-emission microscope (LTEM) system is proposed and developed for inspecting electrical faults in integrated circuits (IC). We test a commercial operational amplifier while the system is operating. Two-dimensional terahertz-emission images of the IC chip are clearly observed while the chip is scanned with a femtosecond laser. When one of the interconnection lines is cut, the damaged chip has a LTEM image different from that of normal chips. The results indicate that the LTEM system is a potential tool for IC inspection.

Imaging of large-scale integrated circuits using laser terahertz emission microscopy

We present the redesign and improved performance of the laser terahertz emission microscope (LTEM), which is a potential tool for locating electrical failures in integrated circuits. The LTEM produces an image of the THz waves emitted when the circuit is irradiated by a femtosecond laser; the amplitude of the THz emission is proportional to the local electric field. By redesigning the optical setup and improving the spatial resolution of the system to below 3 microm, we could extend its application to examining of large-scale integration circuits. As example we show the THz emission pattern of the electric field in an 8-bit microprocessor chip under bias voltage.

Laser terahertz emission microscope for inspecting electrical failures in integrated circuits

The inspection and fault analysis of semiconductor devices has become a critical issue with increasing demands for quality and reliability in circuits as stated in L. A. Krauss et al. (2001), K. Nikawa (2002) and K. Nikawa et al. (2003). Recently, we have developed a laser-terahertz (THz) emission microscope (LTEM) that can be applied for the noncontact and nondestructive inspection of the electrical faults in circuits presented in K. Nikawa et al. (2003). The LTEM can image the amplitude profile of the THz wave emitted by scanning the sample with femtosecond (fs) laser pulses. The amplitude of the THz emission generated by the transient photocurrent is proportional to the local electric field at the laser-irradiated area according to T. Kowa et al. (2003). Therefore, the LTEM image of the semiconductor device while it operates reflects the electric field distribution in the chip. By comparing the LTEM image of a damaged chip with that of a normal one, we can localize the electrical faults. In this work, we report experimental results on a biased 8-bit microprocessor, as well as unbiased MOSFETs embedded in a test element group (TEG).

A Terahertz Chemical Microscope to Visualize Chemical Concentrations in Microfluidic Chips

Here, a new type of terahertz chemical microscope (TCM) is proposed and developed, and the first demonstration of imaging the chemical concentration in fluid channels is reported. Fluid samples flow through channels possessing a semiconductor sensing plate as a bottom wall. Terahertz (THz) waves are radiated from the sensing plate as a result of femtosecond laser illumination. Because the amplitude of the THz radiation depends on the concentration of ions adsorbed on the surface of the plate, the ion distribution in the fluid channels can be visualized by scanning the laser across the plate. An image showing separated solutions with two different proton concentrations is successfully observed as the first demonstration of this instrument.

Laser terahertz emission system to investigate hydrogen gas sensors

A laser terahertz emission system is proposed to investigate the catalytic metal/semiconductor interfaces of hydrogen sensors. Samples were fabricated by depositing a catalytic metal thin film on a semi-insulating silicon substrate. A femtosecond laser was used to radiate terahertz waves from the sample in a gas cell filled with a hydrogen and nitrogen gas mixture. The peak amplitude of the terahertz waves decreased with increasing hydrogen concentration. We also fabricated a metal-oxide-semiconductor field effect transistor hydrogen sensor, and compared its properties with the terahertz radiation properties. These results suggest that the laser terahertz emission system is a potential tool to investigate catalytic metal/semiconductor interfaces.

Resonant terahertz radiation from Tl2Ba2CaCu2O8+δ thin films by ultrafast optical pulse excitation

We have observed the free-space radiation of the resonant terahertz wave from c-axis oriented Tl2Ba2CaCu2O8+δ thin films by femtosecond optical pulse excitation under a radial magnetic field of about 100 Oe nearly parallel to the c axis of the thin film. The observed wave form showed clear oscillations up to 80 K. The frequency was shifted from ∼620u2009GHz at 24 K to ∼300u2009GHz at 80 K, corresponding to an increase in c-axis penetration depth, λc, from ∼26u2009μm to ∼53u2009μm, and disappeared above TC as expected for the Josephson plasma resonance.

Magnetic property mapping system for analyzing three-dimensional magnetic components

A magnetic measurement system utilizing a vector magnetic sensor for analyzing and mapping low frequency magnetic properties of metals has been developed for nondestructive evaluation. The measurement system consists mainly of an induction coil which can expose a large sample area, a vector magnetic sensor for detecting magnetic fields emanating from a sample, a lock-in amplifier, and a two-dimensional scanning stage. The system was determined to have a high magnetic sensitivity corresponding to less than 1nT in the locked-in state. The magnetic field strength change was detected in a sample that contained a slit of width greater than 1mm. Time sequential vector component (normal and tangential) maps were developed. An iron plate as an example of a ferromagnetic metal and an aluminum plate as an example of a good conducting and nonferromagnetic material were compared using this system. Analyzing the vector component maps could differentiate differences in the magnetic properties, such as permeability, edd...

Development of a Compact Moving-Sample Magnetometer Using High-Tc Superconducting Quantum Interference Device

We developed a compact moving-sample magnetometer that uses a high-temperature superconductor–superconducting quantum interference device (high-Tc SQUID) to directly measure the flux coupled to a normal detection coil from a samples magnetic moment in the presence of an external DC magnetic field. The moving-sample method is employed by inserting the sample between the poles of a DC electromagnet and vibrating the sample along the axis perpendicular to the external field axis using an actuator at a frequency of 2.693 Hz. First, the magnetic field of the sample is transferred by a first-order differential normal Cu coil to a SQUID for detection. Then, the SQUID output is fed to a lock-in amplifier for detection. The critical feature of the system design is the use of high-Tc SQUID, which enables the realization of a compact system. The basic characteristics of the developed system are presented, and the current system exhibited a detection limit of 1×10-7 emu.

Partial and macroscopic phase coherences in an underdoped Bi2Sr2CaCu2O8+δ thin film

A combined study using the time-resolved pump-probe technique and the time domain terahertz transmission spectroscopy has been carried out to investigate the normal-state anomalies in underdoped Bi2Sr2CaCu2O8 + δ. It was observed that a superconducting gap and a pseudogap coexist in the superconducting state. The pseudogap locally evolves below T* 210 K simultaneously with the appearance of partial phase coherence with a short lifetime less than 1 ps. With decreasing temperature, the domains with a pseudogap developed and saturated at TS ~ 95 K, and the frequency-dependent superconductivity fluctuation appeared as cooperative phenomena among the partial phase-coherent domains. These experimental data show that the development of the partial coherent local domains with a pseudogap has an important role to switch from the partial to the macroscopic phase-coherent state.

Tetrahertz Pulse Radiation Properties of a Bi2Sr2CaCu2O8+δ Bowtie Antenna by Optical Pulse Illumination

We demonstrate, for the first time, terahertz (THz) pulse radiation properties from a current biased Bi2Sr2CaCu2O8+δ (BSCCO) bowtie antenna by femtosecond laser pulse illumination. The bias current, excitation laser power and temperature dependence of the radiated amplitude of THz pulse are basically in good agreement with those observed on YBa2Cu3O7-δ (YBCO). However, the detailed properties of the THz pulse from BSCCO are considerably different from those for YBCO. The observed amplitude of the terahertz (THz) radiation pulse was very strong due to the small index value of BSCCO thin film even for the small bias current, and the Fourier components of the pulse contains the frequencies lower than 0.4 THz with a central frequency around 0.1–0.16 THz reflecting its long relaxation time of photo-excited quasi-particle in BSCCO.