17.4 The DARPA Diverse Accessible Heterogeneous Integration (DAHI) Program: Convergence of Compound Semiconductor Devices and Silicon-Enabled Architectures

The DARPA Diverse Accessible Heterogeneous Integration (DAHI) program is developing transistor-scale heterogeneous integration processes to intimately combine advanced compound semiconductor (CS) devices, as well as other emerging materials and devices, with high-density silicon CMOS technology. This technology is currently enabling RF/mixed signal circuits with revolutionary performance. For example, InP HBT + CMOS technology is being utilized in advanced DACs and ADCs with CMOS-enabled calibration and self-healing techniques for correcting static and dynamic errors in situ. Such CMOS-enabled self-healing techniques are expected to more generally enable improved CS-based circuit performance and yield in the presence of process and environmental variability, as well as aging. DAHI is also expected to enable the integration of high power CS devices with silicon-based linearization techniques to realize highly power efficient transmitters. By enabling this heterogeneous integration capability, DAHI seeks to establish a new paradigm for microsystems designers to utilize a diverse array of materials and device technologies on a common silicon-based platform. 1 The compound semiconductor (CS) electronics industry has a long history of driving advancements in RF/mixed signal systems. A number of major RF/mixed signal achievements, including large-scale phased arrays [1], satellite communications [1], commercial mobile telephones [2], and solid-state RF power electronics [3] have been made possible using CS materials such as GaAs, InP, and GaN. The success of CS materials in these systems is due in large part to the many superior properties of these materials relative to silicon. For example, high electron mobility and peak velocity of InP-based material systems have resulted in transistors with fmax above 1THz [1][4] as well as ultra-high-speed mixed-signal circuits (see, for example, [5]). The wide energy bandgap of GaN has enabled large voltage swings as well as high breakdown voltage RF power devices [6]. Excellent thermal conductivity of SiC also makes tens of kilowatt-level power switches possible [7]. Additionally, on-chip high-Q microelectromechanical resonators and switches in various The views opinions, and/or findings contained in this article/presentation are those of the author/presenter and should not be interpreted as representing the official views or policies, either expressed or implied, of the Defense Advanced Research Projects Agency or the Department of Defense. materials, such as AlN, have been demonstrated that potentially can be used for clock references and frequency selective filters [8]. However, despite the advantages of CS materials, Si CMOS-based technologies have increasingly been employed in high-performance RF/mixed signal systems. These technologies have leveraged the enormous investments in digital CMOS device scaling and process development to achieve tremendous levels of complexity and integration, while also demonstrating far higher levels of yield and manufacturability than any CS technology. Additionally, scaling has driven device speeds of RF CMOS [9] and SiGe HBTs [10] into the multi-100 GHz regime, albeit at the expense of breakdown voltage. The integration density of Si-based technologies has enabled novel on-chip digital correction and linearization techniques (for example, [11]), producing excellent RF and mixed-signal circuit performance despite the limitations of silicon’s material properties. Such correction techniques have the potential to produce dramatic RF and mixed-signal performance improvements in CS electronics as well; however, CS technologies lack the integration density and yield to implement these circuit concepts. Given these trends, it is our view that the future of high-performance RF and mixed-signal electronics lies in the integration of compound semiconductors with silicon technology in a way that will allow the advantages of the two technology types to be optimally combined. As an example of the potential benefits of heterogeneous integration, consider the plot of Johnson figure of merit (product of transistor cutoff frequency and breakdown voltage) [12] versus integrated circuit complexity (as measured by transistor count) for several semiconductor material and device types, as shown in Figure 1. Si CMOS is by far the superior technology in terms of integration complexity, exceeding the most advanced CS material (InP) by over five orders of magnitude. However, its Johnson figure of merit is exceeded by several CS device types by an order of magnitude. Nitride-based semiconductor devices (represented by GaN in Figure 1) possess the highest Johnson figure of merit of currently utilized semiconductor materials; however, nitrides have only 17 343 CS MANTECH Conference, May 19th 22nd, 2014, Denver, Colorado, USA small-scale integration complexity to date. CS materials such as GaN and InP would benefit greatly from leveraging novel silicon-enabled circuit or system architectures to enhance the performance of advanced CS-based RF/mixed signal circuits.