The Keithley Model 238 is a high-precision, high-current Source-Measure Unit (SMU) designed for characterization of semiconductor devices, materials, and electronic components. It offers four-quadrant operation, acting as a bipolar voltage or current source while simultaneously measuring current or voltage. Fully guarded and supporting both 2-terminal and 4-terminal remote sensing, the Keithley 238 delivers high accuracy, low noise, and flexible sweep sequencing.
Specifications
General
| Parameter | Value |
|---|---|
| Interfaces | IEEE-488 (GPIB) |
| Display | 10-character alphanumeric LED display with 3-character exponent |
| Warm-up Time | 1 hour to rated accuracy |
Physical
| Parameter | Value |
|---|---|
| Power Supply | 90-125 V AC or 180-250 V AC (rear panel switch selectable), 47-63 Hz, 350 VA maximum |
| Operating Temperature | 0°C to 50°C |
| Dimensions (W×H×D) | 133 mm H × 435 mm W × 448 mm D |
| Weight | 11.1 |
| Cooling | Forced air (internal fan) |
Source Specifications
| Parameter | Value |
|---|---|
| Voltage Source Range | ±100 µV to ±110 V |
| Current Compliance (Voltage Source) | Up to 1 A (except 100 mA on the 110 V range) |
| Current Source Range | ±100 fA to ±1 A |
| Voltage Compliance (Current Source) | Up to 110 V (except 15 V on the 1 A range) |
| Voltage Noise (0.1 - 10 Hz) | <3 ppm of range (110 V and 11 V ranges), <10 ppm of range (1.1 V range) peak-to-peak typical |
| Voltage Wideband Noise | 8 mV p-p typical (0.1 to 20 MHz) |
| Voltage Sourcing Overshoot | <0.01% (110 V step, 10 mA range) |
| Voltage Sourcing Settling Time | <500 μs to 0.01% (110 V step, 10 mA range) |
| Current Noise (0.1 - 10 Hz) | <3 ppm of range (<20 ppm on 1 nA and 10 nA ranges, <200 ppm on 1 A range) peak-to-peak |
| Current Sourcing Overshoot | <0.01% typical (10 mA step, RL = 10 kΩ) |
| Current Sourcing Settling Time | <500 µs to 0.01% (10 mA step, RL = 10 kΩ) |
Measurement Specifications
| Parameter | Value |
|---|---|
| Voltage Measurement Range | ±10 µV to ±110 V (except 15 V on the 1 A range) |
| Current Measurement Range | ±10 fA to ±1 A (except 100 mA on the 110 V source range) |
| Normal Mode Noise Rejection (NMRR) | >60 dB at 50 or 60 Hz (with LINE CYCLE integration time selected) |
| Common Mode Noise Rejection (CMRR) | >120 dB at DC, 50 or 60 Hz (with LINE CYCLE integration time selected) |
| Voltage Input Impedance | >10^14 Ω paralleled by <20 pF (as a voltmeter) |
| Current Output Impedance | >10^14 Ω paralleled by <20 pF (on 1 nA range) |
| Maximum Common Mode Voltage | 200 Vpeak |
Guard and Sense Characteristics
| Parameter | Value |
|---|---|
| Sensing Configurations | 2-terminal (local) or 4-terminal (remote sense) |
| Remote Sense Drop Correction | Corrects for up to 2 V drop in each output lead |
| Maximum Remote Sense Lead Resistance | 100 Ω per sense lead for rated accuracy |
| Residual Output Resistance (Voltage Source) | <100 mΩ |
| Guard Output Resistance | <100 mΩ |
| Maximum Guard Output Current | ±2 mA |
| Guard Open Circuit Offset | ±1 mV maximum relative to output HI |
| Floating Output Capability | Up to ±200 V from ground |
Sweep, Timing, and Triggering
| Parameter | Value |
|---|---|
| Sweep Waveform Types | Fixed Level, Linear Stair, Logarithmic Stair, Pulse, Linear Stair Pulse, Logarithmic Stair Pulse |
| Waveform Operators | CREATE, APPEND, MODIFY |
| Minimum Source-Delay-Measure Cycle Time | 1 ms |
| IEEE-488 Source Response Time | 10 ms |
| Internal Buffer Measurement Rate | 1 ms per point |
| Continuous Measurement Speed | 110 readings per second (source DC value over IEEE-488 bus) |
| Trigger Latency Time | <2 ms |
| Load Capacitance Stability | Stable into 20,000 pF typical |
| Logarithmic Sweep Density Options | 5, 10, 25, or 50 points/decade |
| Fixed Level Sweep Parameters | LEVEL, COUNT, DELAY, BIAS |
| Linear Stair Sweep Parameters | START, STOP, STEP, DELAY, BIAS |
| Logarithmic Stair Sweep Parameters | START, STOP, POINTS/DECADE, DELAY, BIAS |
| Pulse Sweep Parameters | LEVEL, COUNT, T_ON, T_OFF, BIAS |
| Linear Stair Pulse Sweep Parameters | START, STOP, STEP, T_ON, T_OFF, BIAS |
| Logarithmic Stair Pulse Sweep Parameters | START, STOP, POINTS/DECADE, T_ON, T_OFF, BIAS |
Environmental
| Parameter | Value |
|---|---|
| Storage Temperature Range | -25°C to 65°C |
| Operating Humidity Range | 0% to 70% RH (non-condensing) up to 35°C; derate 3% RH/°C from 35°C to 50°C |
| Temperature Coefficient | %b1(0.1 %d7 accuracy spec) / %b0C (0%b0C to 18%b0C & 28%b0C to 50%b0C) |
Data Storage
| Parameter | Value |
|---|---|
| Internal Memory Capacity | 1000 readings |
Timing
| Parameter | Value |
|---|---|
| Source Delay Range | 0 to 65000 ms in 1 ms steps |
Connectivity
| Parameter | Value |
|---|---|
| Output Connections | 3-slot triaxial connectors (rear panel) |
| Trigger Input | BNC connector, TTL-compatible |
| Trigger Output | BNC connector, TTL-compatible |
Power Limits
| Parameter | Value |
|---|---|
| Maximum Output Power | 15 W |
Sourcing Resolution & Accuracy
| Parameter | Value |
|---|---|
| Minimum Voltage Source Resolution | 100 µV |
| Minimum Current Source Resolution | 100 fA |
Measurement Resolution & Accuracy
| Parameter | Value |
|---|---|
| Minimum Voltage Measurement Resolution | 10 µV |
| Minimum Current Measurement Resolution | 10 fA |
Pulse Mode
| Parameter | Value |
|---|---|
| Pulse Width Range | 150 µs to 65.5 ms |
| Maximum Pulse Duty Cycle | 10% (at 1 A) |
Power Specifications
| Parameter | Value |
|---|---|
| Maximum Power Consumption | 270 VA |
| Line Frequency | 50 Hz / 60 Hz |
Technology
Source-Measure Unit (SMU)
Applications
Semiconductor characterization, electronic component testing, materials research