1. Overview

1.1 Introduction

The Ark Metrica SMU-4000 Source-Measure Unit (SMU) is a four-channel precision instrument designed for sourcing and measuring voltage and current. Combining the functionality of a voltage source, current source, voltmeter, and ammeter into a single device, the SMU is ideal for applications requiring precise electronic characterisation, including semiconductor testing, material's research, and device evaluation.

Unlike traditional power supplies or standalone measurement instruments, the SMU-4000 operates in both source and measure modes simultaneously. It supports four-quadrant operation, meaning it can source and sink bipolar voltages and currents, making it suitable for characterising both active and passive components under various operating conditions.

Equipped with four independently controllable channels, each with multiple operational modes and flexible compliance settings, the SMU-4000 offers exceptional control for laboratory and production environments. Its remote control options via standard communication protocols ensure seamless integration into automated test systems.

This manual provides detailed instructions on the operation, configuration, and best practices for using the SMU effectively.

1.2 Specifications

Measurement

• Number of independent channels: 4
• Voltage range: ± 5 V
• Voltage DAC set resolution*: 16-bit
• Voltage ADC measure resolution*: 16-bit
• Current range: ± 0.2 A
• Current DAC set resolution*: 16-bit
• Current ADC measure resolution*: 16-bit

* See "Section 1.11 Integration time" for further details.

Communication

• Interfaces: RJ45 (10/100BT)
• IP configuration: DHCP
• Programming: Custom command set based on a subset of SCPI

Power supply

• Input voltage: 12 VDC
• Maximum input current (continuous): <1.6 A (1.6 A internal fuse)
• Maximum input current (transient): 2A

1.3 Front panel

The SMU-4000 front panel, shown in Figure 1.3.1 presents a keyed 16-pin IDC header that allows connections from the SMU channels to be make to device test fixtures using appropriate cables.

The pin numbering for the IDC header is shown in Figure 1.3.2 and descriptions of each pin's functionality is given in Table 1.3.1.

1.4 Rear panel

The SMU-4000 rear panel, shown in Figure 1.4.1 presents power and communications connections.

The power connection should be made to the 2-pin input labelled "12 VDC, 2 A MAX." using the the terminal block provided. Note the input voltage polarity markings when connecting the power supply.

The RJ45 port labelled "Ethernet" provides the communications interface.

The USB interface is for factory use only and should not be connected under normal operation.

1.5 Powering the instrument

The SMU-4000 is powered via the two-pin power connector on the rear panel of the instrument from a 12 VDC supply and requires up to 1.6 A continuous current at maximum load.

The most convenient way to power the instrument is via a PoE+ (IEEE 802.3at) compliant network switch (e.g. TP-Link TL-SL1218MP), ethernet cable, and splitter (e.g. Linovision POE-SP01). The network switch also allows for communication with the instrument from the control computer.

Ensure the input voltage polarity matches the rear panel markings when connecting the DC power supply.

1.6 Calibration

Each SMU channel has been factory calibrated at 23°C ± 2°C. If an instrument requires recalibration please contact Ark Metrica for a quotation at info@arkmetrica.com.

1.7 Cooling fan

The SMU-4000 enclosure contains a cooling fan on the rear panel that expels air pulled in through vents on the front panel. Always ensure there is adequate space for air flow on both ends of the enclosure.

WARNING: BLOCKING THE INLET AND/OR OUTLET VENTS MAY INVALIDATE THE CALIBRATION AND/OR DAMAGE THE INSTRUMENT.

1.8 Compliance

The SMU-4000 provides current and voltage compliance settings to protect devices under test (DUTs) and ensure controlled operation during source and measurement activities. Compliance — also known as limiting — prevents the instrument from exceeding a user-defined maximum voltage or current. This feature is crucial when working with sensitive components, preventing damage due to excessive power levels.

When the SMU is configured to source either voltage or current, the corresponding compliance limit restricts the opposing parameter:

• Voltage Source Mode

  • A current compliance limit is set to prevent excessive current flow.
  • The SMU outputs a user-specified voltage.
  • If the DUT attempts to draw more current than the limit allows, the SMU automatically switches to source the compliance current, preventing the voltage from the increasing further. If under this condition the voltage drops below the user-specified set point, the output will return to sourcing voltage.

• Current Source Mode

  • A voltage compliance limit is set to prevent excessive voltage application.
  • The SMU outputs a user-specified current.
  • If the DUT requires a voltage beyond the compliance limit to supply the requested current, the SMU automatically switches to source the compliance voltage, preventing the current from increasing further. If under this condition the current drops below the user-specified set point, the output will return to sourcing current.

The output does not turn off when in compliance but instead regulates the source to prevent exceeding the limit. Measurement readings will reflect the actual limited output rather than the originally programmed setpoint. When in compliance, the compliance bit will be set in the status byte (see "Chapter 2. Programming Guide" for details). This automatic regulation ensures that the DUT operates within safe limits while allowing accurate characterisation.

1.9 Input limits

WARNING: DO NOT CONNECT A POWER SOURCE TO THE INSTRUMENT FRONT PANEL IDC CONNECTOR THAT CAN SOURCE |V| > 5 V AND/OR |I| > 0.2 A. THIS MAY DAMAGE THE SMU.

1.10 Four-wire voltage sense

The SMU-4000 supports four-wire voltage sensing, also known as Kelvin sensing, to eliminate errors caused by lead resistance when measuring low voltages or sourcing precise currents. Unlike traditional two-wire measurements, which include the resistance of the test leads in the measurement, four-wire sensing uses separate force and sense connections to provide accurate voltage readings directly at the device under test (DUT).

In a two-wire configuration, the same pair of leads is used to source current and measure voltage. However, the resistance of these leads introduces a voltage drop, particularly at high currents, leading to inaccurate voltage measurements.

In a four-wire configuration, separate pairs of leads perform sourcing and sensing:

• Force Leads: Supply current or voltage to the DUT.
• Sense Leads: Measure the voltage directly at the DUT, eliminating errors from lead resistance.

Since the sense leads carry negligible current, the voltage drop across them is minimal, ensuring the SMU measures the true voltage applied to the DUT.

In addition to improving measurement accuracy, the SMU-4000 also provides output feedback when sourcing voltage in four-wire mode. The feedback mechanism sets the force terminals of the SMU to apply whatever voltage is necessary to achieve the user-specified set voltage at the sense terminal connections to the DUT. This eliminates the impact of lead resistance errors in both setting and measurement of applied voltage.

However, note that the force terminals are limited to supplying ± 5 V. If high voltages are requested by the user and the DUT draws a high current, it may not be possible to increase the force voltage high enough to achieve the user-set voltage at the sense terminals because of the voltage drop in the external force circuit test leads. It is always recommended to keep the test lead resistance as low as possible to minimise the impact of this effect.

1.11 Integration time

The SMU-4000 allows the user to specify measurement integration time in Number of Power Line Cycles (NPLC). The integration time window is the period over which each SMU channel averages samples from its analog-to-digital converters (ADCs). The measurement result is an average over as many samples as the ADCs can measure within the integration time. This means the effective measurement resolution depends on the user-specified NPLC.

1.12 Default settings

See "Chapter 2. Programming Guide" for default values of each user settable parameter.

1.13 Remote communication

The SMU-4000 supports remote communication over an Ethernet network using the TCP/IP suite. A host computer can establish a connection to the SMU via its assigned IP address and communicate with individual measurement channels through dedicated TCP ports.

The SMU-4000 obtains its IP address dynamically from a Dynamic Host Configuration Protocol (DHCP) server on the local network. To enable communication with the SMU, a DHCP server must be present and operational.

It is strongly recommended to configure the DHCP server to assign a static IP lease based on the SMU’s Media Access Control (MAC) address, ensuring the instrument maintains a consistent IP address for reliable operation. Each SMU-4000 unit has its own MAC address, which is printed on a label located on the rear panel of the device. This MAC address follows a locally administered format: 02:0A:0E:XX:XX:XX. Here, the XX:XX:XX portion is unique among devices provided by Ark Metrica. Since these MAC addresses are not globally unique, there is a potential risk of MAC address conflicts in network environments where similar address schemes are used. To prevent possible network conflicts:

• The SMU-4000 could be used on a dedicated or controlled local network.
• Consider using Virtual Local Area Networks (VLANs) if integration into an enterprise environment is necessary.

Once an IP address has been assigned, the SMU-4000 provides individual TCP/IP sockets for each measurement channel, allowing them to be controlled independently and perform measurements in parallel. Each channel is accessed via a specific TCP port number, as detailed in Table 1.13.1.