C-V measurement technology, skills and pitfalls-C-V measurement technology connection and calibration

Although many C-V measurement techniques are relatively simple in themselves, it is not so simple to connect the C-V tester to the probe station in a way that can ensure measurement quality. At present, there are many kinds of manipulators and probe cards used in probe stations. When we try to support I-V, C-V and pulsed or ultra-fast I-V measurements at the same time on a probe station, they will bring some practical problems. When performing I-V, C-V or ultra-fast I-V measurements, the quality of the measurement results is directly related to the quality of the cable and the configuration of the probe station used.
DC I-V measurement [1] adopts low-noise coaxial cable and remote detection line. C-V measurement requires the use of a coaxial cable with a remote detection line, and the length of the cable must be very controlled. The ultra-fast I-V test requires a 50 ohm coaxial cable, but the remote detection cable brings the problem of impedance mismatch to the ultra-fast I-V test. RF C-V measurement requires the use of special RF cables, probes with "ground-signal-ground" structure, and calibration bases. Unfortunately, these wiring methods are not compatible with other methods.


Figure 4. Probe configuration of American Probe & Technologies
Through the experiment in the laboratory of Keithley [2], we chose the probe configuration (73 series or 74 series) provided by American Probe & Technologies (as shown in Figure 4). Its advantage is that most probe stations provide Goods vendors have supplies. This special probe is coaxial, with a Kelvin connection. The main body and shielding layer are floating, so it can be used as drive protection for I-V measurement, or short ground path for C-V and ultra-fast I-V measurement by jumper connection. The connector on this type of probe is called SSMC. There are three types of cables that can be used to achieve high-quality connections with this type of probe: SSMC to triaxial cable connection is suitable for DC IV measurement and general applications (direct or indirect connection), SSMC to coaxial cable connection can be used for CV Or ultra-fast IV test [3] (indirect connection), and the more special SSMC to SMA cable connection can achieve CV measurement performance, especially at higher frequencies (direct connection). Figure 4 shows the dual-probe configuration scheme for C-V measurement; each probe is connected to a pair of coaxial cables to realize remote Kelvin detection connection. Note that the jumper between the two probe bodies is very short. This jumper ensures a good ground connection between the probes, which is very important for high-frequency measurements.