Wafer scale millimeter-wave integrated circuits based on epitaxial graphene in high data rate communication

www.nature.com/scientificreports OPEN received: 22 August 2016 accepted: 28 December 2016 Published: 01 February 2017 Wafer scale millimeter-wave integrated circuits based on epitaxial graphene in high data rate communication Omid Habibpour1, Zhongxia Simon He1, Wlodek Strupinski2, Niklas Rorsman1 & Herbert Zirath1 In recent years, the demand for high data rate wireless communications has increased dramatically, which requires larger bandwidth to sustain multi-user accessibility and quality of services. This can be achieved at millimeter wave frequencies. Graphene is a promising material for the development of millimeter-wave electronics because of its outstanding electron transport properties. Up to now, due to the lack of high quality material and process technology, the operating frequency of demonstrated circuits has been far below the potential of graphene. Here, we present monolithic integrated circuits based on epitaxial graphene operating at unprecedented high frequencies (80–100 GHz). The demonstrated circuits are capable of encoding/decoding of multi-gigabit-per-second information into/ from the amplitude or phase of the carrier signal. The developed fabrication process is scalable to large wafer sizes. To meet the fast growing demand for telecommunication services, developing high-data-rate communication links in the range of multi-gigabit per second (Gbps) is necessary. The high speed data links can be implemented using either wireless or fiber optic technologies. Wireless technology, particularly in urban areas, has several advantages over fiber optics such as mobility, universal deployment, short installation time and cost effectiveness. However, to achieve data rates comparable to that of the fiber optics, there is a need to develop wireless systems with a very large bandwidth (∼10 GHz). This may be achieved by operating at millimeter wave (mm-wave) frequencies (30–300 GHz)1. Even though mm-wave covers a broad range of frequencies, only a certain part of the spectrum is suitable for wireless transmission. This is because atmospheric absorption is only relatively small in these so-called atmospheric windows. The mm-wave atmospheric windows are centered at 35, 90, 140 and 220 GHz2. There is therefore a special interest in the 90 GHz band since it simultaneously offers a low loss medium and a large band width (up to 30 GHz). Hence, development of electronic circuits operating in this band is a huge step forward for the realization of multi-Gbps wireless links. In this regard, graphene is a promising material for the development of mm-wave electronics due to its excellent electron transport properties. Recently, there is a rapid progress in the development of graphene field effect transistors (G-FETs). G-FETs with intrinsic current-gain cutoff frequencies (fT) of 400 GHz and maximum oscillation frequency (fMAX) of 100 GHz have been demonstrated3,4. In addition, many G-FET based circuits including frequency multipliers5–8, mixers6,9–12, amplifiers13–16 and power detectors17–20 have been presented. Most of the demonstrated circuits so far are not integrated circuits (ICs) requiring external circuitries for operation. ICs allow for high frequency and complex circuits but at the cost of laborious fabrication process. At mm-wave frequencies, broadband circuits can practically only be realized in IC technology. Up to now, there are only few demonstrations of graphene based ICs performing complex wireless communication functions such as signal modulation and demodulation (encoding/decoding information into/from a carrier signal)21–24. The operating frequency of the presented ICs is mainly restricted to a few GHz which is far below the potential of graphene. In addition, the demonstrated data rate is limited to tens of megabits per seconds (Mbps) which is too low for high data rate communications. To compete with existing technologies in high frequency applications, graphene films should exhibit 1 Chalmers University of Technology, Gothenburg 41296, Sweden. 2Institute of Electronic Materials Technology, Wolczynska 133, 01-919 Warsaw, Poland. Correspondence and requests for materials should be addressed to O.H. (email: ) Scientific Reports | 7:41828 | DOI: 10.1038/srep41828 1 www.nature.com/scientificreports/ Figure 1. Graphene based high data rate communication landscape. (a) A perspective view of high data rate link based on graphene transmitter (Tx) and receiver (Rx). (b) Fabricated chip on a 70-μm thick SiC (chip size: 15 × 15 mm2) consists of frequency mixer ICs (left, circuit size: 1.35 × 1.1 mm2) and integrated power detector ICs (right, circuit size: 1.35 × 0.7 mm2). a high carrier mobility as well as a low sheet resistance. These properties can be found in hydrogen intercalated epitaxial graphene on silicon carbide (SiC) substrate25. Even though processing ICs on SiC substrate is very challenging, it paves the way for the realization of graphene based high speed data communications. Here, we present results on monolithic mm-wave IC (MMIC) based on epitaxial graphene in high data rate applications in the 90 GHz band. The developed process is scalable up to full wafer sizes. Currently the limiting factor is not the wafer size but the uniformity of available epitaxial graphene resulting in about 70% yield. The fabricated MMIC has different circuits elements capable of receiving and retrieving information embedded in the amplitude and phase of the carrier signal at the rate of 4 Gbps. Furthermore, the developed circuits are highly linear allowing to generate modulated signal up to the rate of 8 Gbps at 90 GHz band with a bit-error-rate (BER) below 10−5. The operating frequency is about 20 times higher and the achieved data rate is more than 200 times better than the previously reported graphene based IC24. This work elevates graphene based radio frequency (RF) ICs’ performance to the level that start competing with the existing matured technologies. Results Epitaxial graphene. Typically, the term “epitaxial graphene” refers to graphene grown on SiC which is in fact not done by epitaxy but by sublimation of silicon. In this study graphene is grown by traditional Chemical Vapor Deposition (CVD) epitaxy using carbon precursor or more accurately by Vapor Phase Epitaxy (VPE)25. This method enables the growth of carbon layers directly on SiC surface on both silicon (Si) and carbon (C) polarities with the precision of synthesizing a pre-defined number of carbon layers. The CVD graphene has been studied for both Si-terminated and C-terminated SiC, however, more attention is directed to Si-face growth due to its higher accuracy. To reduce the substrate effect on the synthesized graphene, hydrogen atoms are intercalated and consequently quasi-free-standing (QFS) graphene26 is formed. QFS-graphene exhibits much higher and temperature independent carrier mobility, which is desirable for high-speed electronics. The carrier mobility and sheet resistance in our ma (...truncated)