Ultra-High-Isolation Mutual-Embedded Transformer in Organic Substrate for Digital Isolator

In this letter, an ultra-high-isolation mutual-embedded transformer in organic substrate (METOS) of digital isolators is proposed and demonstrated for ultra-high isolation and excellent transmission performances simultaneously. At the micro-electromechanical system (MEMS) scale, the METOS adopts coupling coils completely embedding in isolation material for the first time. With an area of 1.16 mm2, the METOS, fabricated on a 1-mm silicon wafer using MEMS processes, has $100~\mu \text{m}$ thick isolation layers between each turn of the primary and secondary coils. The METOS has achieved an excellent transformer efficiency over a wide band of 80–720 MHz, and its transformer efficiency is 89.55% at 374 MHz. The METOS isolation capability of more than 7.5 kV has also been measured. The ultra-high isolation and excellent transmission performances of the METOS, are very promising for efficient high-voltage isolated signal transfer applications.

I. Introduction

Isolators are widely used in aerospace, electric vehicles, and high voltage transmission to isolate high voltage circuits, transmit signals, and protect electronic equipment [1], [2], [3], [4]. Smaller size and better performance are increasingly required. In particular, the highly integrated isolated gate driver system of power on-chip applications needs isolators to be compact and provide high-voltage signal isolation [5], [6], [7], [8]. Traditional applied isolators are opto-isolators using optical technique [9], [10], which have limitations of the lifetimes of LED’s light emission, the ranges of operating temperature, and data rates [11], [12]. Therefore, digital isolators have been developed. Digital isolators use capacitive [13] or transformer techniques [11], which are called capacitive digital isolators and electromagnetic digital isolators. However, capacitive digital isolators are weak to isolate high voltage, and not suitable for power transfer [14], [15]. Electromagnetic digital isolators have both high voltage isolation and low sensitivity to noise [16], [17], [18].