Description
Impedance mismatch between the STNO device (for MTJs 100 – 1000 Ohm) and standard RF circuitry (at 50 Ohm) leads to a reduction of the output power of 10 dB. Proper impedance matching is thus important.

Partners
LETI/DCOS ; LETI/DACLE

Financing
ANR-05-NANO-44 MagICO (2005-2008) ; OSEO/Anvar (2005-2009) ; Carnot RF (2006-20010) ;

Objectives
Integration of STNOs into conventional RF circuitry means that the STNO has to deliver 0dBm to drive conventional microwave components. To avoid reduction in output power due to impedance mismatch the group of LETI/DACLE has developed a high impedance amplifier on a 130 nm CMOS process. This amplifier is composed of three stages respectively, see Fig. 1 : (a) a high impedance entrance to extract the full voltage signal ; (b) a voltage amplification stage of 22 dB ; (c) a conversion stage to match the output to 50 Ohm.

Latest results
Output power measurements have been performed on two hybrid configurations (STNO chip and amplifier chip each of them wire bonded to the same platform, see Fig. 1) to demonstrate the enhancement of the output power. In the first configuration the STNO is buffered by a standard 50 Ohm input amplifier and in the second configuration by the high input impedance amplifier. From Fig. 2 it is clear that the impedance matching allows a gain of 6 to 11 dB on the output power, depending on the frequency, thus improving the “power issue” that is inherent to the STNOs.

Staff
Pierre Vincent (LETI/DACLE) Patrick Villard (LETI/DACLE) Hichem Louazani (SPINTEC) Jean-Phillipe Michel (LETI/DCOS) Dimitri Houssameddine (SPINTEC) Ursula Ebels (SPINTEC) Marie-Claire Cyrille (LETI)

Related content
IEEE JOURNAL OF SOLID-STATE CIRCUITS 45, 214 (2010), P. Villard et al.

Figure 1

High impedance amplification : Top, schematics of the three stage amplifier. Bottom, photograph of the experimental setup. The STNO is bonded to the amplifier

Figure 2

Experimental results comparing the output power when buffered by a high impedance amplifier and a commercial 50 Ohm input impedance amplifier