Switches
Replacing PhotoMOS switches in automatic test equipment applications
By Edwin Omoruyi, senior applications engineer, Analog Devices Abstract
This article introduces the replacement of PhotoMOS switches with CMOS switches in automated test equipment (ATE) houses. The CMOS switches not only match the performance benefits of PhotoMOS in terms of capacitance-by-resistance (CxR) merit but also offer superior turn-on speed, reliability, and scalability, making them well-suited for the evolving needs of ATE houses in the era of advanced memory testing.
Introduction
The growing demand for high performance memory, particularly high bandwidth memory (HBM), in artificial intelligence (AI) applications is driving more complex chip designs. Automatic test equipment (ATE) houses, which are critical in verifying these components, are now facing increased pressure to keep pace with this demand. Traditionally, in memory wafer probe power supply applications, PhotoMOS switches find use due to their favourable low capacitance- by-resistance (CxR) merit. CxR merit is a reduction in signal distortion, improving switch off-isolation and offering fast switching speeds and low insertion loss.
Despite these advantages coupled with the high stand-off voltage, PhotoMOS switches have certain limitations. These limitations include reliability, scalability, and turn-on speed. The slow turn-on speeds have been a notable point of dissatisfaction among customers.
To address these challenges, Analog Devices, Inc. (ADI) has developed switches to replace PhotoMOS in memory wafer probe power supply applications. The ADI switches provide fast turn-on speeds and possess the same low CxR merit, ensuring efficient switching. Furthermore, the scalability of these switches improves test parallelism, allowing ATE setups to manage more extensive and faster testing processes. These features
22 October 2025
Figure 1 demonstrates how switches can facilitate the creation of a matrix configuration, enabling one PMU to evaluate multiple DUTs. This configuration enhances the flexibility and scalability of ATE systems by reducing the need for multiple PMUs and wiring complexity, which is crucial for high volume or multi-device testing setups.
Switch architectures Figure 1. PMU switching applications.
To understand the evaluation study (that is, the comparison done between a PhotoMOS switch and a CMOS switch using developed hardware evaluation boards) and the subsequent results gathered, it is necessary to show benchmark comparisons between a PhotoMOS switch and a CMOS switch. The best place to start is with the switch architectures for both.
While the architectures for a CMOS switch and PhotoMOS switch appear to be different, Figure 2 shows the off capacitance (COFF) when the switches are off. This parasitic capacitance is across the input source pin and the output pin.
Figure 2. PhotoMOS and CMOS switch architectures.
make ADI switches a strong alternative to PhotoMOS, especially as ATE houses strive to meet the growing demands for efficient and high-performance memory testing in AI-driven applications.
Application diagram
In ATE setups, switches play a crucial role in facilitating the testing process by allowing the connection and disconnection of multiple devices under test (DUTs) to a single measurement instrument, such as a
Components in Electronics
parametric measurement unit (PMU). As described, switches enable the PMU to force specific voltages toward various DUTs and to sense current feedback from these DUTs efficiently. Switches streamline the testing process, particularly in scenarios where multiple DUTs require evaluation in parallel or sequentially. The ability to direct voltage from the PMU to multiple DUTs, along with sensing currents from them, optimises test throughput and minimises the need for reconfiguration of test setups between tests.
For a PhotoMOS switch, the COFF is between the drain output pins. In addition, the PhotoMOS switch has input to output capacitance (or drain capacitance) as well as an input capacitance on the light emitting diode (LED) stage used for the turn-on and turn-off of the output MOSFETs.
For a CMOS switch, the COFF is between the source and the drain pins. In addition to the COFF, there are the drain capacitance (CD) and source capacitance (CS) to ground for a CMOS switch. These capacitances to ground are also a complaint point received from customers using CMOS switches.
When either switch is enabled to pass input signals through to the output, the on-resistance (RON) is across the source and the drain pins. By understanding
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