Co-integration of Enhancement and Depletion Modes of GaN-based Transistors for Next Generation RF Communication Circuits – ED-GaN

In today’s fast evolution and expansion of wireless communications, the GaN HEMT is a good candidate, taking advantage of its high frequency performance, high breakdown voltage and material robustness. For the next generations of RF power amplifiers, GaN-based technology is the most promising to satisfy more demanding specifications of the market. The standard GaN-HEMT is a depletion mode device (normally-on). RF circuit designers claim for normally-off devices (enhancement-mode) integrated with depletion-mode ones in the same chip to reduce circuit complexity and power consumption. According to literature, many research teams have worked in the development of enhancement-mode devices by different means. Among many proposed methods to deplete the channel at gate bias = 0 V, the most promising for device commercial production are: A) Fluorine (F- ions) implantation in the upper part of GaN barrier layer to deplete the channel B) Gate recess on a thick barrier layer C) Etching of the barrier layer using an etch-stop layer D) Local epitaxy of p-GaN layer on the top of the barrier layer. All of these aforementioned techniques are currently being investigated in research labs. Each technique has its own advantages and disadvantages. So far, it is not clear which of them (A-D) is the one that provides the best combination of device performance, reproducibility and reliability. Furthermore, the monolithic integration of enhancement and depletion mode GaN-based HEMTs, fabricated on the same wafer is a great challenge. The reason is that the epitaxial structures are generally designed to foster one of the two modulation modes (enhancement or depletion), which are sometimes conflicting. This situation generates risks for any foundry that wants to bring the integrated ED-mode devices into the RF market without making the choice of the best depletion-mode technology. The objective of this project is integrating high performance, reproducible and reliable enhancement-mode GaN HEMTs with the depletion-mode devices on the same chip. The consortium will perform an assessment of these four depletion mode approaches (A-D) to bring RF device innovation based on a nonpartisan investigation. To accomplish this, the industrial partner (OMMIC) and the four research institutions (LN2, IEMN, CRHEA, IMS) have designed a 42 month scientific program that includes device design, epitaxial growth, microfabrication, performance evaluation and reliability testing. Then, the consortium will select the best integrated enhancement-depletion mode approach answering OMMIC’s specification. This path represents a major difference compared to what is presently reported at the state-of the art. After the project is completed, the technology will be transferred to OMMIC’s foundry. One of the most important advantages of this project is that the most promising technologies to fabricate ED-mode GaN HEMTs are going to be tested under the same conditions, reducing the risk of making an inadequate technology choice. Therefore, OMMIC will be in a winning position and will have an excellent opportunity to make a breakthrough, becoming a world-class leader in GaN RF circuits. The commercial success of the product will have a positive impact to the manufacturer (OMMIC) and on upstream and downstream companies, allowing the creation of new jobs and prosperity in the related sectors. Defense, health equipment, consumer electronics, the automotive industries are vast markets for this technology. They are strategically important for economic development, security, safety and well-being of our society. Furthermore, due to the highly experimental characteristic of this project and the exceptional capabilities of the consortium, the project will produce an outstanding scientific impact in the wide-bandgap semiconductor domain.