Millimeter-Wave Circuits

mHEMT Technology

All monolithic microwave integrated circuits (MMICs), which are required to realize the high frequency components, were manufactured using Fraunhofer IAF metamorphic high electron mobility transistor (mHEMT) technology. The mHEMT features an Indium Gallium arsenide (InGaAs) channel with high Indium content for an excellent noise characteristic similar to Indium Phosphide (InP) based HEMTs, but is grown on a conventional Gallium Arsenide (GaAs) wafer. To adapt the different lattice parameters, a metamorphic buffer layer is grown between the GaAs substrate and the active device layers. The high electron mobility in the channel and the better charge confinement, due to larger band offsets, make the mHEMT technology the most appropriate device for high frequency and ultra-low-noise applications while simultaneously being cost efficient, due to the use of GaAs wafers.

 

T-Gate
© Fraunhofer IAF

T-Gate of a 100nm-Transistors

The mHEMT layers are grown on 4˝ semi insulating GaAs wafers by molecular beam epitaxy (MBE). To suppress parasitic substrate modes, the technology features a backside process, where the wafers are thinned down to a final thickness of 50 μm. Subsequently, through-substrate vias to the front side are processed by dry etching and finally, the wafer backside is gold plated. In addition to the active devices, metal-insulator-metal (MIM) capacitors, NiCr thin film resistors and airbridge technology are provided for circuit layout, as well as microstrip or grounded coplanar waveguides (GCPW) as transmission lines. Fraunhofer‑IAF manufactures mHEMTs with gate-lengths of 100 nm, 50 nm, 35 nm and 20 nm.

 

Radar MMIC for Modul 2

MMIC
© Fraunhofer IAF

MMIC for module 2.

The MMIC of module 2 is realized as a single chip, containing the signal conditioning as well as the RF processing stage of the received echo signal. Therefore, an off-chip generated signal at about 15 GHz is used, which is first of all frequency multiplied into W-band. A major fraction of the signal is amplified using a power amplifier and coupled to the antenna port. On the RF PCB, a single Vivaldi antenna is used as a combined transmitting and receiving antenna. The separation of the transmitted and received signal is carried out by an integrated Lange coupler on the MMIC. The received signal is than amplified using a low-noise amplifier and split in-phase to feed an I/Q-mixer. The local oscillator port (LO) of the mixer is generated by a fraction of the transmitted signal, which is split 90° out of phase using a second Lange coupler.

Further Information:

Metamorphic HEMT technology for low-noise applications
Leuther, A.; Tessmann, A.; Kallfass, I.; Losch, R.; Seelmann-Eggebert, M.; Wadefalk, N.; Schafer, F.; Gallego Puyol, J.D.; Schlechtweg, M.; Mikulla, M.; Ambacher, O. In: Indium Phosphide & Related Materials, 2009. IPRM '09. IEEE International Conference on , vol., no., pp.188-191, 10-14 May 2009

35 nm metamorphic HEMT MMIC technology
Leuther, A.; Tessmann, A.; Massler, H.; Losch, R.; Schlechtweg, M.; Mikulla, M.; Ambacher, O. In: Indium Phosphide and Related Materials, 2008. IPRM 2008. 20th International Conference on , vol., no., pp.1-4, 25-29 May 2008

20 nm metamorphic HEMT WITH 660 GHZ FT
Leuther, A.; Koch, S.; Tessmann, A.; Kallfass, I.; Merkle, T.; Massler, H.; Loesch, R.; Schlechtweg, M.; Saito, S.; Ambacher, O. In: Compound Semiconductor Week (CSW/IPRM), 2011 and 23rd International Conference on Indium Phosphide and Related Materials , vol., no., pp.1-4, 22-26 May 2011