Development of Millimeter-Wave High Power Density Diamond-Collector Heterojunction Bipolar Transistors
Abstract
The overarching theme of DREaM in the high power technical track, TA1, is to enable high dynamic range applications by showing revolutionary performance metrics in high power, PAE, and linearity at the device level. Although the program is clearly focused on materials and devices, it is instructive to begin by translating the dynamic range application demands into how we envision the devices would ultimately be deployed in circuits. A key limiting physical trade-off for dynamic range is to achieve high power amplification at the maximum possible voltage swing (signal). The most common example of this trade for power is in GaN FET technology when scaling the drain voltage results in huge current swings. For this reason, our approach is to focus on meeting the program goals through a new class of HBTs that maximizes common base amplifier performance because this configuration ties power gain directly to voltage gain in devices with inherently high power densities and that operate at higher voltages. Our proposed devices uses a wide band gap p- diamond collector/p+ diamond subcollector together with an AlGaAs(p)/GaAs(n) emitter/base structure that is transferred to the diamond substrate before HBT fabrication. This pnp HBT has critical features that directly address the power scaling challenge presented by DREaM and directly impacts dynamic range. First, the lightly doped diamond collector provides a trade space for achieving a high collector breakdown voltage HBT. This is in contrast to scaling for raw speed which is achieved through extremely high collector current densities (charging time) and is actually the opposite of the goal of having high dynamic range. The second feature is the conductivity of the n-type GaAs base. The base allows for two critical improvements for power scaling and dynamic range. Having very low base sheet resistance (we have a factor of >100 improvement over SOA InP HBTs because they are npn) means that we can build wider devices so that in terms of total power we can avoid current crowding and use fewer fingers. The current level and total periphery are both key issues with simply trying to trade frequency bandwidth when power scaling. The highly doped base also puts our proposed device into a similar regime as modern SiGe HBTs. Our proposed diamond-collector HBT also involves two of our three main innovative claims. The diamond substrate, p+ subcollector, and p- collector are a unique capability to this team through the MSU/CCD partnership. Our team has proven capability in diamond materials development across substrates, epitaxy, and doping. In addition, this process requires high quality diamond polishing which is a critical element for our approach and a notoriously difficult process, but one in which we have expertise. Having a vertically integrated materials supply for diamond makes our approach feasible. As we will show, through recent work on high power Schottky diodes at MSU we have already demonstrated many of the key elements required by our device design and processing methods. The second key innovation is the use of a transfer-printed AlGaAs/GaAs structure for the emitter-base junction. UW and UB have an established record in transfer processing and pre-existing IP in this area. We will show data from prior work on devices with Si/Ge transferred to diamond and prior work with GaAs transferred to Si and to GaN. This process the enabling technology for making an HBT after substrate transfer and transferring an already processed HBT which, to date, is very expensive and yields poorly.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 23, 2018
- Source ID
- N000141812032
Entities
People
- John D. Albrecht
Organizations
- Michigan State University
- Office of Naval Research
- United States Navy