What is the method for measuring the electrical characteristics of bipolar junction transistors (BJTs) ?

An example of a measurement circuit for electrical characteristics (cut-off current, current gain, saturation voltage) described in the data sheet is shown. 
Please refer to the FAQ (What are the electrical characteristics of bipolar junction transistors (BJTs) ?) for the explanation of each item.
The electrical characteristics explained here are described in the data sheet as shown in Table. 1.

The measurement method for each item is shown below. Semiconductor characteristics are greatly affected by temperature. It is necessary to consider fluctuations not only due to room temperature but also due to losses (voltage and current) during measurement. In addition to controlling the room temperature at the time of measurement, please consider the time to apply voltage and current. Pulse measurement is recommended to suppress the temperature rise of the transistor.

Table. 1: Electrical characteristics Bipolar junction transistor (BJT) 2SC2712
Table. 1: Electrical characteristics Bipolar junction transistor (BJT) 2SC2712

1. Collector cut-off current ICBO: Fig. 1

It is an electrical characteristic paired with the collector-base voltage VCBO described in Absolute Maximum Ratings. With the emitter open, apply a voltage so that the pn junction between the base and collector is reverse biased, and measure the current. Since the voltage VCB applied between the collector and the base is the absolute maximum rated voltage, care must be taken so that the voltage value does not exceed the specified value. ICBO is the leakage current between the collector and the base, so it fluctuates depending on the temperature.

2. Emitter cut-off current IEBO: Fig. 2

It is an electrical characteristic paired with the collector-base voltage VEBO described in the absolute maximum ratings. With the collector open, apply a voltage so that the pn junction between the base and emitter is reverse biased, and measure the current. Since the voltage VEB applied between the emitter and base is the absolute maximum rated voltage, care must be taken so that the voltage value does not exceed the specified value. IEBO is the leakage current between the emitter and base, so it varies with temperature.

Fig. 1: Collector cut-off current measurement circuit
Fig. 1: Collector cut-off current measurement circuit
Fig. 2: Emitter cut-off current measurement circuit
Fig. 2: Emitter cut-off current measurement circuit
Fig. 3: DC current gain measurement circuit
Fig. 3: DC current gain measurement circuit

3. DC current gain hFE: Fig. 3

Apply the specified voltage VCE between the collector and emitter and adjust the voltage VBE between the base and emitter so that the target collector current IC is obtained. The base current IB at this time is measured, and the result of the calculation of the following formula is hFE. 　hFE ＝ IC / IB
Note that hFE is temperature dependent. (Fig. 4)
As shown in Fig. 5, hFE changes due to the Early effect. High frequency transistors with narrow base widths will have a larger change.

Fig. 4: h<sub>FE</sub> – I<sub>C</sub> curve (effect of temperature) 2SC2712
Fig. 4: hFE – IC curve (effect of temperature) 2SC2712
Fig. 5: I<sub>C</sub> - V<sub>CE</sub> curve (Early effect) 2SC2712
Fig. 5: IC - VCE curve (Early effect) 2SC2712

4. Collector-emitter saturation voltage　VCE(sat)： Fig. 6

In the circuit shown in Fig. 6, first apply a voltage of about 0.6 V between the base and emitter with the voltage source VBE. After that, the collector current IC is applied while gradually increasing until the specified current is reached. Next, change the base voltage VBE until the base current IB reaches the specified value. Measure the collector-emitter voltage VCE when IB reaches the specified current. This voltage is VCE(sat).
If the current source on the collector side is applied while the transistor is off, it may become an abnormally high voltage and destroy the transistor. Set the open-circuit voltage of the current source in advance so that it is less than the collector-emitter voltage VCEO described in the absolute maximum ratings.
VCE(sat) is temperature dependent (Fig. 7).

Fig. 6: Collector-emitter saturation voltage measurement circuit
Fig. 6: Collector-emitter saturation voltage measurement circuit
Fig. 7: V<sub>CE(sat)</sub> – I<sub>C</sub> curve (effect of temperature) 2SC2712
Fig. 7: VCE(sat) – IC curve (effect of temperature) 2SC2712

5. Base-emitter saturation voltage　VBE(sat)： Fig. 8

First, apply a voltage of about 0.6 V between the base and emitter with the voltage source VBE. After that, the collector current IC is applied while gradually increasing until the specified current is reached. Next, adjust VBE so that the base current IB is the default, and measure the voltage between the base and emitter at this time. This voltage is VBE(sat).
If the current source on the collector side is applied while the transistor is off, it may become an abnormally high voltage and destroy the transistor. Set the voltage when the current source is open so that it is less than the collector-emitter voltage VCEO described in the absolute maximum ratings.
VBE(sat) is temperature dependent (Fig. 9).
This characteristic VBE(sat) is a spec that makes a pair with collector-emitter saturation voltage (Table. 2).

Fig. 8: Base-emitter saturation voltage measurement circuit
Fig. 8: Base-emitter saturation voltage measurement circuit
Fig. 9: V<sub>BE(sat)</sub> – I<sub>C</sub> curve (effect of temperature) 2SC5354
Fig. 9: VBE(sat) – IC curve (effect of temperature) 2SC5354
Table. 2: Electric characteristics Excerpt 2SC5354
Table. 2: Electric characteristics Excerpt 2SC5354

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