Ultra-Low-Noise Cryogenic High-Electron-Mobility Transistors K. H. GEORGE DUH, MEMBER, IEEE, MARIAN w. POSPIESZALSKI, SENIOR MEMBER, IEEE, PHILLIP M. SMITH, MEMBER, IEEE, LUKE F. LESTER, JAMES M. BALLINGALL, MEMBER, IEEE, AND SANDER WEINREB, FELLOW, IEEE WILLIAM F. KOPP, PIN HO, MEMBER, IEEE, AMANI A. JABRA, PANE-CHANE CHAO, MEMBER, IEEE, zyx Abstract-Quarter-micrometer gate-length HEMT’s for cryogenic low-noise application with very low light sensitivity have been devel- oped. At room temperature, these exhibit a noise figure of 0.4 dB with associated gain of 15 dB at 8 GHz. At a temperature of 12.5 K the minimum noise temperature of 5.3 zyxwvutsrq f 1.5 K has been measured at 8.5 GHz, which is the best noise performance ever observed for any mi- crowave transistors. The results clearly demonstrate the great poten- tial for low-temperature low-noise applications. I. INTRODUCTION N RECENT YEARS, high-electron-mobility transis- I tors (HEMT’s) have been demonstrated to show supe- rior noise performance to conventional MESFET’s. Noise performance of 0.25-pm HEMT’s and MESFET’s fabri- cated in the GE laboratory are compared in Fig. 1 over 8-60 GHz at room temperature. HEMT’s not only have lower noise figures, they also have several characteristics that make them more attractive for low-noise applications than the MESFET’s. The scattering parameters (S-param- eters) of a HEMT in a zyxwvutsr 50-Q system exhibit lower zyxwvut 1 zyxwvutsrqponmlkjihgfe S,, 1 and higher I S,, 1 values than those for a MESFET of the same size, providing inherently better output match and larger gain-bandwidth product. In addition, a HEMT has much lower noise conductance, zyxwvuts g, and usually a lower ra- tio Xgopt/Rgopt (where Rgopt -t jXgopt is the optimum source impedance) than the comparable MESFET [ 11 to facilitate lower noise over a broad bandwidth. Another advantage of the HEMT is that its performance improves more rap- idly with cooling than does that of the MESFET. This is due to the enhancement of electron mobility by reduced ionized impurity scattering in HEMT structures resulting from spatial separation of the channel electrons and their parent ions in the highly doped AlGaAs layer. Manuscript received September 8, 1987. The HEMT devices were de- veloped at the General Electric Company with the support of the Jet Pro- pulsion Laboratory, California Institute of Technology, under Contract 957352, monitored by S. Petty. The National Radio Astronomy Observa- tory is operated by Associated Universities, Inc. under contract with the National Science Foundation. K. H. G. Duh, W. F. Kopp, P. Ho, A. A. Jabra, P.-C. Chao, P. M. Smith, L. F. Lester, and J. M. Ballingall are with the Electronics Labo- ratory, General Electric Company, Syracuse, NY 13221. M. W. Pospieszalksi and S. Weinreb are with the National Radio As- tronomy Observatory, Charlottesville, VA 22903. IEEE Log Number 8718789. 5 40 zyxwvu 60 100 10 20 Frequency (GHz) Fig. 1. Comparison of noise performance for 0.25-pm HEMT’s and MES- FET’s at room temperature. For good low-noise devices, one must have good pin- choff characteristics, low parasitic resistances zyx Rg and R, ( R,, the gate metallization resistance and R,, the series source resistance that includes the ohmic contact resis- tance and the channel resistance between gate and source contacts), and high transconductance g, . For a field-ef- fect transistor, the minimum noise temperature can be ap- proximately expressed by [4] where zyxwv K and K, are noise coefficients, t = T,/290, and T, is the physical temperature of the device. The first term represents the effective noise voltage generator in the in- put circuit and is dominated by the thermal noise of R, and R,. The second term represents that portion of the nonthermal noise coupled to the gate circuit, which is un- correlated with the drain current. For the cryogenic op- eration (T, < 20 K and t < 0.07), the second term K,/gi becomes dominant. Therefore, for a good cry- ogenic low-noise device, the wafer should have a proper doping concentration and spacer thickness to achieve an enhancement of g, at low temperature. Another important factor is the crystal quality, especially the presence of de- fects at the layer interfaces and in doped AIGaAs, giving rise to light sensitivity of the device dc parameters and noise performance. 0018-9383/88/0300-0249$01 .OO zyxwvut O 1988 IEEE Authorized licensed use limited to: UNIVERSITY OF NEW MEXICO. Downloaded on October 24, 2008 at 17:38 from IEEE Xplore. Restrictions apply.