Hassan Tanbakuchi

Nanoscale materials and device characterization via a scanning microwave microscope

The vector network analyzer (VNA) architecture as it exists today has the ability to measure impedances close to the analyzers own characteristic impedance (i.e., 50 ohms) with good precision up to 100GHz stimulus frequency. However, the measurement precision and resolution provided by a VNA drop by two orders of magnitude as impedance deviates from 50 ohms. We propose a solution that remedies the lack of measurement precision and resolution for large and small impedances when measured by a VNA. A new scanning microwave microscope (SMM) that utilizes a half-wavelength resonator in conjunction with a diplexer connected to a VNA to perform very sensitive capacitance measurements at the tip of a conductive atomic force microscope (AFM) is discussed. These measurements are achieved via transformation of the high impedance (i.e., the very small capacitance between the AFM tip/sample to the ground) to 50 ohms (i.e., the measurement systems characteristic impedance) using a half-wavelength resonator and diplexer.

Semiconductor Material and Device Characterization via Scanning Microwave Microscopy

The advent of the new nano-scale high speed materials and devices require metrology tools capable of characterization at the operating frequency range with nano-scale resolution. The non-destructive measurement of dopant profile and carrier concentration in 2D and 3D are critical in the new emerging materials and devices such as carbon nanotubes, graphene, nanowires and spintronics. A new Scanning Microwave Microscope (SMM) has been developed to characterize the material and devices at microwave frequencies with nanometer resolution. The SMM has been shown to be capable of quantitative characterization of metals, semiconductors and dielectrics.

Scanning Impedance Probe Microscope

A new sensitive scanning impedance probe microscope (SIPM) that uses have a wavelength resonator with conjunction with a diplexer connected to a vector network analyzer (VNA), which can perform a very sensitive capacitance measurement at the tip of a conductive atomic force microscope is the subject of this invention. This is achieved through transformation of the high impedance (very small AFM tip capacitance between tip and sample to ground) to 50 Ohm (or any other systems characteristic impedance) through a half a wavelength resonator and diplexer. The VNA measurement architecture as exists today has the capability of measuring impedances close to the characteristic impedance of the analyzer (i.e. 50 Ohms) to a good precision and up to 100 GHz stimulus frequency .The precision and resolution of the DUT (device under test) impedance markedly drops as it deviates from 50 ohms by a couple of order of magnitudes specially in the case of the capacitance between the AFM tip and sample to the ground. We are proposing a solution which remedies the lack of precision and resolution for large and small impedances (small capacitance) when measured by existing VNA.

attoF MOS varactor RF measurement VNA coupled with interferometer

Nowadays with capabilities offered by advanced silicon technologies both for design above 60GHz and for high performance Digitally Controlled Oscillator, the use of sub fF varactor is mandatory. One of the challenge to develop this device is to be able to characterize it accurately for process optimization and modeling. In high and above all low frequency range, this type of measurement has to face with the issue of high impedance characterization and mismatch regarding 50Ω. In the RF range, Agilent is developing an interferometer module added to a VNA able to characterize very low capacitance. In this paper, we evaluate this equipment using dedicated calibration silicon structures to measure 500aF MOS varactor and compare measurement to developed electrical model.

Quantitative measurement of electric properties on the nanometer scale using atomic force microscopy

We describe a method to measure capacitances and dopant densities with a nanometer scale spatial resolution. It is implemented using an atomic force microscope with a conductive tip interfaced with a microwave vector network analyzer. A microwave signal is sent to the tip and the ratio of reflected and incident wave is measured. The technique - also referred to as scanning microwave microscopy (SMM) - can be calibrated to yield quantitative measurements of the capacitance at the tip sample junction. On semiconductor surfaces SMM can be used to measure dopant density distribution quantitatively.