Wireless communications rely on high-frequency signal transmission, which is a challenge for electrostatic discharge (ESD) protection. Why is this the case?

Because high-frequency interface chips are very fragile and have very low requirements for parasitic capacitance values, there are few anti-static part numbers to choose from. Today, we will provide you with a solution based on your on-site tests. This customer selected the Shanghai Leiditech ultra-low capacitance polymer PESD-PESD0521U005H for the antenna interface. The anti-static capability of this part number can reach ±30KV when in contact with air. This is an ultra-low capacitance polymer PESD part number with a working voltage of 5V. The test results are fine, but the customer has a question. What is the working principle of this device? How to select the type? Besides being used in antennas, where else is it used?

A. What is a polymer PESD

The core functional material of polymer PESD devices is a precisely designed conductive polymer composite material. It is not a single material but a multi-component and multi-level microstructure system. Its core is a voltage-sensitive nonlinear resistor. Its composition can be summarized as: polymer matrix + functional conductive filler + additive + electrode and encapsulation

The "P" in PESD stands for Polymer: It emphasizes the essence of its polymer matrix, which is different from ceramics (MLV) and semiconductors (TVS).

B. Working principle

The working principle of polymer PESD devices lies in their "voltage-triggered nonlinear resistance variation", and its working principle can be clearly understood from both micro and macro levels. :

1、Microscopic Mechanism: The "Smart Switch" of Nanonetworks

The core inside the device is nano/micron-sized conductive particles uniformly dispersed in the polymer matrix (which is non-conductive).

1) Normal state (high resistance state, off)

The conductive particles are separated by extremely thin polymers, forming a large number of nanoscale gaps. Under normal voltage, electrons find it very difficult to cross these gaps, and only an extremely small current can "slip through". Therefore, the device has extremely high resistance and almost no leakage, functioning as if it were invisible in the circuit.

2) ESD event trigger (low resistance state, conduction)

When high-voltage static electricity strikes, an extremely strong electric field is generated at the nanoscale gap. The electric field will thin the "wall" that hinders electrons, allowing them to pass through the wall on a large scale (quantum tunneling). In an instant, all the particles are connected through the electron tunnel, forming a three-dimensional conductive grid. The device's resistance plummets by a million to a billion times within one nanosecond, transforming into an ultra-low resistance channel that rapidly discharges static electricity.

3) Event ended (Self-recovery)

After the static electricity is discharged, the electric field disappears and the electron "wall-penetrating" effect stops immediately. The elasticity of the polymer restores the gap and disconnects the conductive grid. The device resistance automatically and rapidly returns to a high-resistance state, preparing to deal with the next shock.

2、Macroscopic characteristics: Nonlinear V-I characteristic curve

The microscopic mechanism directly determines the macroscopic current-voltage relationship of the device, which is the core characteristic of it as a protective component.

When the voltage is lower than the trigger value, the device resistance is extremely high and the current is almost zero. Once the voltage reaches the threshold, the device immediately conducts in an avalanche manner. After entering the conducting state, the voltage is firmly locked at a very low level (clamped), and even if the current increases, the voltage hardly rises. After the danger is eliminated, the device automatically returns to high resistance.

C.  Application

The application of PESD devices is determined by their advantages of ultra-low capacitance and fast response, mainly serving ESD protection for high-speed data lines and RF signal lines.

1、Ultra-high-speed data interface

USB 3.0/3.1/4.0, Thunderbolt, HDMI 2.0/2.1: These interfaces have speeds up to 10Gbps or even over 40Gbps. The capacitance of PESD devices is usually less than 0.5pF, and can even reach 0.05pF. The insertion loss and signal distortion introduced are extremely small, making it the only reliable choice to ensure signal integrity.

2、Rf antenna port:

GPS antennas, Wi-Fi/ Bluetooth antennas, 4G/5G cellular antennas, NFC antennas: The antenna ports have extremely high requirements for impedance matching. Any parallel capacitance will cause frequency disharmony and performance degradation. The ultra-low capacitance characteristic of PESD makes it the standard solution for antenna ESD protection.

3、High-speed digital bus

MIPI D-PHY/C-PHY (for cameras and displays), LVDS, Ethernet: On these buses that are sensitive to signal quality, PESD can provide transparent protection.

4、Key interfaces for portable devices:

The headphone jacks, microphones, buttons, side connectors and other components of smartphones, tablets and laptops are widely applied due to their thinness, low capacitance and good protection performance.

The principle of application: PESD devices come into play in any situation where the signal frequency is high, the parasitic capacitance is extremely sensitive, and robust ESD protection is required.

D.  The differences between low junction Capacitance Polymer PESD and low junction Capacitance TVS and selection decisions

Although all three pursue "low capacitance", their physical essence, performance limits and best application are completely different.

l  Low junction capacitance polymer ESD suppressor: A natural "supercar", designed for ultra-fast signals, with the lowest capacitance (up to 0.05pF), but relatively weak power (energy tolerance).

l  Low junction capacitance TVS: A compact “special force”, it reduces capacitance through technical optimization while maintaining precise clamping and good protection strength, making it an all-round player.

Detailed comparison table of two low-capacity ESD devices

l  The flowchart of the selection decision

According to your design requirements, you can quickly select based on the following logic:

E. Shanghai Leiditech Polymer PESD commonly used part numbers

The following is a list of some of the polymer PESD part numbers of Leiditech for your reference. If you have any needs, please contact the Leiditech EMC team or the Leiditech sales staff.