CIPT Method

The Current-In-Plane Tunneling (CIPT) method is a way of measuring the properties of a tunnel junction by placing a set of probes on a full wafer/large sample without  conventional techniques for structuring of tunnel junctions. This greatly speeds up development and testing. Also, these non-invasive measurements are local in nature due to the very small (micron sized) probe spacing, which can be used for homogeneity control as well as characterization of a parameter varying over a wafer sized sample.

In CIPT measurements, the (sheet) resistance of a sample is measured using a four-point-probe method. A current is sent through a sample by two probes (I+ and I-), and from the induced voltage drop between two other probes (V+ and V-) the resistance of the sample can be calculated. In the figure below (a) represents the top view of the sample, while (b) represents a cross section of the sample.

Schematic of the CIPT method

If the sample is a tunnel junction, a part of the current will flow through the top electrode, while another part will tunnel through the barrier and flow through the bottom electrode. The amount of current tunneling through the barrier can be changed by changing the distance between the probes, as is shown in the figure below.

Resistance as a function of the number of probes

When the probes are placed very close together the current will not `have time’ to tunnel down and will mainly flow through the top electrode. When the probes are very widely spaced, the current will divide proportionally between the top and bottom electrode. Therefore, the resistance of the tunnel junction will be higher for smaller probe spacing, and fall off to a lower value at larger spacing as schematically shown in the graph above. By measuring the resistance of the tunnel junction for different probe spacing (by selecting different electrodes on the CIPT probes), a number of data points along such a curve is obtained. Fitting the data yields the characteristic properties of the tunnel junction.

In the figure above the y-axis represents sheet resistance, while the x-axis represents the distance between probes used for each of the measurements. From this figure the following important parameters can be estimated.

 

R(T) = Resistance of the top electrode.

R(B) = Resistance of the bottom electrode.

RA Product = Indication for the resistance of the tunnel barrier.

λ = Characteristic length.

TMR = The relative change in resistance between the top and bottom electrode.

SmartProber

The SmartProber is SmartTip’s solution for characterization of thin film stacks on a microscopic scale. By using CIPT probes to contact samples, a variety of four point probe measurements can be conducted, including Current-In-Plane Tunneling (CIPT) characterization of a tunnel junction stacks.

Currently, two SmartProber systems are available: the SmartProber-TT is a low cost system especially suited for research and development on in-plane or non-magnetic samples, while the SmartProber-P1 can map 300 mm wafers and boasts a high perpendicular-to-plane magnetic field.

Open source software

To increase versatility, a large part of the SmartProber’s software is open source. This allows the creation of custom measurement routines, changing the user interface and/or data file format to custom standards, or create `smart measurements’ in which the next measurement to perform will change depending on the values measured in previous measurements.

CIPT

Current In Plane Tunneling (CIPT) is a very fast and cost effective method to characterize Magnetic Tunnel Junctions (MTJ’s).

CIPT Method

The Current-In-Plane Tunneling (CIPT) method is used to characterize the properties of a tunnel junction, by landing a probe on top of the sample. These non-invasive measurements greatly speed up development and testing, due to the microsized probe spacings these measurements can be used for both homogeneity control and parameter characterization. Click on this link for further information about the CIPT method. 

Instruments

SmartTip offers several high field, high accuracy instruments for both industry and academia to perform CIPT measurements. Both in-plane and perpendicular field options are available.

CIPT Probes

Our micromachined CIPT probes with different pin configurations are suitable for a variety of applications. Several carrier options are available to fit all CIPT capable instruments.

 

SmartProber-TT

This low-cost table-top equipment comes with manual x-y positioning, fully automated probe landing, an in-plane magnet as well as an anti-vibration table. The open nature, low cost, and versatility make the SmartProber-TT especially suited for research and/or development.

  • Sample size: up to 6″ wafers, up to 1.3 mm thickness
  • In-plane magnetic field up to 40 kA/m
  • RA range 0.5-100k Ωμm2