Capacitance Measurement Basics for Device/Material Characterization

Capacitance Measurement Basics for Device/Material Characterization

Application Notes

Introduction  

The capacitance-voltage (CV) measurement has been one of the most important measurements for investigating the characteristics of the materials and the behavior of the devices. Now the importance of the CV measurement is getting higher in the research and development of the next generation materials and devices such as wide bandgap devices (GaN/SiC), nanodevices, organic devices, MEMS, and so on. The analysis based on the CV measurement is effective for investigating the basic characteristics of the materials and improving the quality of the device.  

When performing the CV measurement, it is very common to perform the current-voltage (IV) measurement at the same time. This application note introduces the key points in the CV measurements including the issues, know-hows, and tips, especially combined with the IV measurements, which are obtained through the long experience of Keysight in the semiconductor measurements. The following topics are covered in this application note.  

  • CV measurement basics 
  • How to make the cable connections.  
  • How to compensate for the error.  
  • Tips for on-wafer measurement.  
  • Keysight solutions for the CV and IV measurement.  

The quasi-static CV (QS-CV) measurement is one of the important CV measurement techniques for the research and development area, too. It is discussed in the other application note. Refer to it, if you are interested in the QS-CV application. 

CV Measurement Basics

This section introduces the basics of the CV measurements for measurement methodology and the cable connections. Basics of the CV measurement methodology There are many ways for performing the CV measurement, but the most popular method in the below 10 MHz frequency range is the auto-balancing bridge-type CV meter as shown in Figure 1.  

It measures the impedance of the device under test (DUT) Zx as Zx = Vx / Ix, where Vx is the AC signal voltage applied to the DUT, and Ix is the AC current flowing through the DUT. The CV meter consists of (1) the AC signal source Vx with the DC bias source in the high terminal, (2) the current Ix flowing through the DUT, and (3) the low terminal vector current meter as shown in Figure 1. 

The high current (Hc) terminal applies the AC measurement signal and the DC bias voltage to the DUT, and the high potential (Hp) terminal senses the actual AC signal applied to the DUT. The low current (Lc) terminal sinks the DUT current through the reference resistor Rr and keeps the Lc potential as close as possible to zero volts (called virtual ground) with the negative feedback loop consisting of the high gain amplifier (Vr) in the low potential (Lc) terminal and the feedback resistor Rr.  

The current flowing through the DUT (Ix) is obtained as Vr/Rr, and the DUT impedance Zx is obtained as Zx = Vx / Ix = Rr (Vx / Vr). This is the basic methodology of the auto-balancing bridge-type CV meter. 

Cable Connection to DUT

To perform the accurate CV measurement, you will need to connect the 4 terminals (Hc, Hp, Lc, Lp) correctly to the DUT, and there are several ways of connections. The following describes the most frequently used two types of cabling methods: one is the four-terminal pair configuration and the other is the shielded two-terminal configuration.