Four-point Sheet Resistance Research Articles

Electrical Contact Properties between the Accumulation Layer and Metal Electrodes in Ultrathin Poly(3-hexylthiophene)(P3HT) Field Effect Transistors

Probing contact properties between an ultrathin conjugated polymer film and metal electrodes in field effect transistors (FETs) is crucial not only to understanding charge transport properties in the accumulation layer but also in building organic sensors with high sensitivity. We investigated the contact properties between gold electrodes and poly(3-hexylthiophene) (P3HT) as a function of film thickness using gated four-point sheet resistance measurements. In an FET with a 2 nm thick P3HT film, a large voltage drop of 1.9 V (V(D) = -3 V) corresponding to a contact resistance of 2.3 × 10(8) Ω was observed. An effective FET mobility of 1.4 × 10(-3) cm(2)/(V s) was calculated when the voltage drop at the contacts was factored out, which is approximately a factor of 3 greater than the two-contact FET mobility of 5.5 × 10(-4) cm(2)/(V s). A sharp decrease in the ratio of the contact resistance to the channel resistance was observed with increasing film thickness up to a thickness of approximately 6 nm, separating a contact limited regime from a charge transport limited regime. The origin of the large contact resistance observed in the device prepared with an ultrathin P3HT film is discussed in light of results from X-ray diffraction (XRD) and atomic force microscopy (AFM) studies.

Comparative study of size dependent four-point probe sheet resistance measurement on laser annealed ultra-shallow junctions

In this comparative study, the authors demonstrate the relationship∕correlation between macroscopic and microscopic four-point sheet resistance measurements on laser annealed ultra-shallow junctions (USJs). Microfabricated cantilever four-point probes with probe pitch ranging from 1.5to500μm have been used to characterize the sheet resistance uniformity of millisecond laser annealed USJs. They verify, both experimentally and theoretically, that the probe pitch of a four-point probe can strongly affect the measured sheet resistance. Such effect arises from the sensitivity (or “spot size”) of an in-line four-point probe. Their study shows the benefit of the spatial resolution of the micro four-point probe technique to characterize stitching effects resulting from the laser annealing process.

Square and collinear four probe array and Hall measurements on metal oxide thin film gas sensors

Gas detection by means of metal oxide semiconductor sensors is ascribed to the change of resistance due to the modulation of the intergrain potential barrier (grain contribution) and of the metal semiconductor barrier at the contacts (contact contribution). We present a method for measuring the contribution of the contact and the grain resistance separately during exposure to CO and CH 4 by employing the square and collinear four probe array (David S. Perloff, Four-point sheet resistance correction factors fot thin rectangular samples, Solid State Electron. 20 (1977) 681–687). The electronic properties are investigated by means of Hall effect measurements according to grain boundary scattering mechanism.

Film properties of Ti/TiN bilayers deposited sequentially by ionized physical vapor deposition

Ionized physical vapor deposition (iPVD) has received much attention as a method for depositing material at the bottom and on the sidewalls of the high aspect ratio features proposed for sub-0.25 micron integrated circuits. In this article, we describe the film properties of Ti/TiN bilayers deposited sequentially using the iPVD technique. The experimental configuration consisted of a planar magnetron sputtering source in combination with an inductively coupled RF plasma. TiN was reactively sputtered from a titanium target which remained non-nitrided throughout the deposition, a process commonly referred to in non-ionized PVD as operating in the non-nitrided mode (NNM). These films were analyzed by cross-sectional scanning electron microscopy and transmission electron microscopy, automated four-point sheet resistance probe, x-ray diffraction, x-ray fluorescence, stress gauge, and Rutherford backscattering. Highly oriented 〈111〉 TiN was observed on 〈002〉 oriented Ti underlayers. At via aspect ratios of 4:1 with vertical sidewalls, bottom coverage approaching 100% was obtained. Varying process parameters did not change the bulk resistivity significantly, and values as low as 23 μΩ cm were measured for the NNM TiN films. Mechanical stress was strongly influenced by substrate temperature, as has been observed for both conventionally sputtered and collimated Ti/TiN. Below 200 °C, the films were highly compressive, but values below 2 GPa were obtained at 400 °C. RF plasma power and pressure were also found to affect stress. Deposition rates of 900 Å/min were measured, corresponding to a specific deposition rate of 1.8 Å/kW s.

Manipulation of the Ti/Si reaction paths by introducing an amorphous Ge interlayer

Evolution of the Ti/a-Ge/Si trilayer reactions has been investigated using transmission electron microscopy and Auger electron spectroscopy. Instead of amorphous phase formation, as usually observed in the Ti/Si bilayer reaction, the crystalline Ti6Ge5 is the first phase observed during the reaction. Preceding the equilibrium C54-Ti(Si,Ge)2, a substitutional solid solution type C49-Ti(Si,Ge)2 forms upon annealing at 550–600 °C, regardless of the replacement of amorphous phase by the crystalline phase. The C49-to-C54 polymorphic transformation occurs at ∼650 °C. The reaction path is also correlated with the change in film resistance obtained from a four-point sheet resistance measurement.

Conductive SnO2/Sb powder: preparation and optical properties

Preparation of an SnO2 semiconducting powder doped with antimony (x=2.38 mol%) was achieved by co-precipitation. The unit cell parameters of the doped SnO2 powders were measured and their changes with dopant concentration were determined. Four-point sheet resistance measurements, together with optical and infrared spectra of the powder were taken in order to obtain a highly-conducting, low-emitting powder which could be used for antistatic paint preparation. Evolution of the phonon bands corresponding to Sn-O stretching modes as a function of dopant concentration were followed, and a model calculation based on an extended four-parametric Kurosawa relation was applied to the reflection spectra of differently doped powders. It was found that the frequency of the plasma oscillations shifts with dopant concentration, and the intensity of the reflectivity peaks was correlated with plasmon-phonon interactions. An additional negative reflection peak in the range 1100 to 1200 cm−1 was found in the reflection spectra of highly doped powders and was attributed to the coupled modes between the plasma oscillations and one of the phonon combinational or overtone modes of SnO2.

The use of four-point probe sheet resistance measurements for characterizing low dose ion implantation

This paper describes two techniques for extending the capabilities of conventional four-point sheet resistance measurements to the characterization of low-dose (10 10−10 13 ions/cm 2) implantation. One technique, which involves the direct measurement of sheet resistance values as great as 100 kΩ/□ utilizes high resistivity substrates in conjunction with a special cleaning procedure for passivating the silicon surface. The second technique relies on the fact that the sheet resistance of an impurity layer will increase significantly when damaged by relatively low implant doses. This technique is extremely sensitive, and can be used for monitoring doses as low as 10 10 frsol| ions/ cm 2 as well as electrically inactive impurities such as silicon, oxygen and argon.

Four-point sheet resistance correction factors for thin rectangular samples

A conformal transformation technique is employed to determine the geometrical correction factor associated with four-point sheet resistance measurements of thin rectangular samples. Results are presented which are useful in identifying sample geometries for which the correction factor is insensitive to the placement of the four electrodes on the interior of the sample. The correction factors for corner-contacted rectangular samples (van der Pauw resistors) are shown to be highly sensitive to small variations in the length-to-width ratio, such as might be experienced when fabricating microelectronic structures. Experimental data which serve to confirm the validity of the analytical solution are provided for several cases of practical interest.