Low-Power Nanowire Circuits and Transistors Dey, Anil 2013 Link to publication Citation for published version (APA): Dey, A. (2013). Low-Power Nanowire Circuits and Transistors. [Doctoral Thesis (monograph), Department of Electrical and Information Technology]. 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LUND UNIVERSITY PO Box 117 221 00 Lund +46 46-222 00 00 Low-Power Nanowire Circuits and Transistors Doctoral Thesis Anil W. Dey Department of Electrical and Information Technology Lund University Lund, Sweden 2013 Academic thesis for the degree of Doctor of Philosophy at the Faculty of Engineering at Lund University which will be defended on Friday, October 4th, 2013, at 10:00 in E:1406, E-building, Ole R(cid:246)mers v(cid:228)g 3, Lund, Sweden Department of Electrical and Information Technology Lund University P.O. Box 118 SE-221 00 Lund Sweden ' Anil W. Dey, 2013 ISSN 1654-790X, No. 51 ISBN 978-91-7473-593-2 (printed version) ISBN 978-91-7473-594-9 (pdf version) Printed in Sweden by Tryckeriet i E-huset, Lund September 2013 How hard can it be? - Jeremy Clarkson Abstract This thesis explores several novel material systems and innovative de- vice concepts enabled by nanowire technology. State-of-the-art fab- rication techniques such as electron beam lithography and atomic layer deposition are utilized to achieve high control and quality in the device fabrication. The devices in this thesis are based on two main types of design geometries, lateral and vertical, each of which have strengths and weaknesses. The (cid:28)rst part of the thesis describes the goals of future metal(cid:21)oxide(cid:21)semiconductor (cid:28)eld-e(cid:27)ect transistors (MOSFETs) and discusses the ultimate scalability surrounding exper- imental results for 15-nm-diameter InAs nanowires and how they com- pare to other state-of-the-art transistors. The extracted on-resistance (R = 250Ω·(cid:181)m) and drive currents (I = 1250(cid:181)A/(cid:181)m) are compa- on on rable to state-of-the-art high-electron-mobility transistors (HEMTs) from MIT and quantum-well (cid:28)eld-e(cid:27)ect transistors from Intel. The outstanding performance is mainly attributed to the reduced access resistance achieved through an n+-i-n+ doping pro(cid:28)le. The extracted mobilities also agree well with state-of-the-art and theoretical predic- vi tions for extremely scaled devices. The second part of the thesis discusses how nanowires may be employed to enable III-V complementary metal(cid:21)oxide(cid:21)semiconductor (CMOS) digital logic. Nanowires enable the formation of both n-type semiconductors and p-type semiconductors, which are a requirement for CMOS, in a single nanowire and allow for integration on a Si platform. III-V MOSFETs are frequently employed for analog ap- plications, but there is a disconnect regarding p-type devices, which are also required for digital logic. The individual segments of the nanowire are evaluated as well as the entire nanowire in an inverter con(cid:28)guration. This thesis then presents a strategy for matching the drive currents n- and p-type MOSFETs. The (cid:28)nal part of the thesis deals with a family of devices that op- erate according to principles fundamentally di(cid:27)erent from those of a traditional MOSFET, namely tunnel FETs (TFETs). There is a de- mand for steep-slope devices such as TFETs to enable supply-voltage scalingtoreducethepowerdissipation. Althoughdeviceshavedemon- strated <60 mV/decade operation, they commonly su(cid:27)er from low on-currents. To maximize the drive current, the broken band gap alignment of GaSb/InAs is exploited to allow for a direct tunneling mechanism. The material system is (cid:28)rst explored as Esaki diodes and in various doping pro(cid:28)les to understand the in(cid:29)uence of doping on device performance. The devices are further evolved into TFETs by the addition of a high-κ gate dielectric and an additional terminal. Experimental results display high on-currents of I = 310(cid:181)A/(cid:181)m on comparable to other state-of-the-art TFETs. Finally, an innovative design concept combining axial and radial heterostructures is utilized to design a radial TFET with a small footprint. A radial GaSb/InAs core/shell TFET provides an attractive way to increase the drive cur- rent of a TFET without compromising either device electrostatics or chip area. The functionality of radial Esaki diodes and TFETs is demonstrated and evaluated by the maximum peak currents, which vii are much improved as compared to their axial counterparts when nor- malized to the largest cross-sectional area of the nanowire, assuming a vertical device geometry, illustrating the advantage of a core(cid:21)shell architecture. The dimensions of the InAs shells are below 15-nm and display clear quantization e(cid:27)ects revealed in low-temperature electri- cal characterization. viii Popul(cid:228)rvetenskaplig sammanfattning Hur hade v(cid:229)r v(cid:228)rld sett ut utan den teknologiska revolutionen som skett de senaste decennierna? Inget internet, inga mobiltelefoner, inga surfplattor? Drivkraften bakom att det hela (cid:228)r en v(cid:228)ldigt liten best(cid:229)ndsdel som sitter i n(cid:228)stan all elektronik, den s(cid:229) kallade transis- torn. En transistor kan se lite olika ut men (cid:228)r i stora drag en elektrisk komponent d(cid:228)r man styr str(cid:246)mmen mellan tv(cid:229) kontakter med hj(cid:228)lp av en tredje kontakt kallad f(cid:246)r gate eller styre. Man kommer inte s(cid:229) l(cid:229)ngt med bara en transistor men n(cid:228)r man b(cid:246)rjar n(cid:228)rma sig ett antal miljarder s(cid:229) kommer man upp i antalet transistorer som sitter i en modern processor. Redan 1925 patenterades den f(cid:246)rsta transistorn av Julius Edgar Lilienfeldmeneftersomupp(cid:28)nnareninteskrevomsinuppt(cid:228)cktin(cid:229)gra vetenskapliga tidsskrifter s(cid:229) uppm(cid:228)rksammades inte uppt(cid:228)ckten. Det var inte f(cid:246)rr(cid:228)n 1947 d(cid:229) William Shockley, John Bardeen och Walter Brattain p(cid:229) AT&T Bell Labs byggde en fungerande transistor baserad p(cid:229) Lilienfelds patent som halvledarutvecklingen verkligen b(cid:246)rjade ta fart. Det kontinuerliga kravet p(cid:229) allt snabbare och energisn(cid:229)lare elek-