Spin nano-oscillator-based wireless communication

Abstract

Spin-torque nano-oscillators (STNOs) have outstanding advantages of a high degree of compactness, high-frequency tunability, and good compatibility with the standard complementary metal-oxide-semiconductor process, which offer prospects for future wireless communication. There have as yet been no reports on wireless communication using STNOs, since the STNOs also have notable disadvantages such as lower output power and poorer spectral purity in comparison with those of LC voltage-controlled oscillators. Here we show that wireless communication is achieved by a proper choice of modulation scheme despite these drawbacks of STNOs. By adopting direct binary amplitude shift keying modulation and non-coherent demodulation, we demonstrate STNO-based wireless communication with 200-kbps data rate at a distance of 1 m between transmitter and receiver. It is shown, from the analysis of STNO noise, that the maximum data rate can be extended up to 1.48 Gbps with 1-ns turn-on time. For the fabricated STNO, the maximum data rate is 5 Mbps which is limited by the rise time measured in the total system. The result will provide a viable route to real microwave application of STNOs.

Figure 1. Operation and test setup of the STNO.

(a) Schematic of the STNO sample with a free layer (FL), a barrier, and a pinned layer (PL). M_p denotes the magnetization of the pinned layer, M_f(r,t) is the magnetization of the free layer, and H_eff is the local effective magnetic field. (b) Schematic of the test setup for the STNO. H_ext is the external magnetic field. Chip photo of the STNO (middle).

Figure 2. Characteristics of the measurements for the fabricated STNO.

(a) Magneto–resistance of the STNO as a function of I_DC (H_ext = 55 Oe). P indicates the parallel (P) state between M_p and M_f, AP denotes the antiparallel (AP) state between M_p and M_f. (b) The oscillation frequency f_osc and peak output power P_peak level of the STNO as a function of I_DC (H_ext = 55 Oe). (c) f_osc and the P_peak level of the STNO as a function of H_ext (I_DC = 3 mA). (d) The linewidth Δf of the STNO as a function of I_DC (H_ext = 55 Oe).

Figure 3. Configuration of the STNO–based binary ASK transceiver.

(a) Schematic of the STNO–based binary ASK transmitter (T_x). (b) Schematic of the receiver (R_x) and the gain and noise figure (NF) of the R_x chain. (c) The measurement set–up of the STNO–based binary ASK system. (d) The received signal power flow, where P_in is the received signal power of R_x and Ant, LNA, RF amp, and BPF are the measurement positions before the R_x antenna, the LNA, the RF amplifier, BPF, and the envelope detector, respectively. The signal level right after BPF is −32.7 dBm, which is within the detectable range of the demodulator (–60 ~ 5 dBm).

Figure 4. Modulated and demodulated signal in the time domain.

(a) The measured time trace of the modulated signal when the pulse frequency is 100 kHz at node a in Fig. 3a. (b) The measured time trace of the demodulated signal of 100 kHz at node b in Fig. 3b.

Figure 5. Rise and fall time of modulated and demodulated signal.

(a) The rise and fall time from the measured time trace of the modulated signal when the pulse frequency is 1 MHz at node a in Fig. 3a. (b) The measured time trace of the demodulated signal of 1 MHz at node b in Fig. 3b. (c) Total rise and fall time of the transceiver from the demodulated signal.