![]() In other words, being the amplification power dependent, we point out that this is a nonlinear amplifier which can have a key role in hybrid CMOS-spintronic systems. A variation of the input power does not induce a proportional change of the output power hence, | S 11 | is not constant but is a nonmonotonic function of the input power, which exhibits a record | S 11 | larger than 2 for P in = −60 dBm. The main result here is the observation of a nonlinear dependence of the amplification rate. 2 and 3.įigure 1d shows | S 11 | as a function of the input power for V dc = −400 mV and H ext = 60 mT (the field value showing the maximum | S 11 | , see Fig. The presence of amplification regions is robust and it has been observed in several devices as shown for example in Supplementary Figs. The peak position and the frequency range where | S 11 | > 1 is tunable with the external field (25 MHz/mT), as one would expect for the behavior of a resonance mode of saturated ferromagnetic sample. The maximum value of | S 11 | = 1.8 is observed at 1.5 GHz for the bias field of 60 mT. The amplification region (| S 11 | > 1) is resonant in nature and is observed for a field amplitude larger than 30 mT and at an input bias voltage larger than the threshold value (see discussion below). For | H ext | above 50 mT, the magnetization is almost aligned with the field, and the resistance tended to saturate at 428 Ω.įigure 1c summarizes | S 11 | as a function of the input frequency for a microwave power P in of −45 dBm at a bias voltage V dc of −400 mV. Where \(\) directions, where the maximum amplification performance for this device is achieved. For those two-terminal devices, the amplification gain can be expressed by the S 11 parameter 7, 8: Recently microwave amplification has been demonstrated with two-terminal MTJs biased with a direct current (dc) and designed with materials that have a large heat-to-spin conversion 7. Since then, spintronic amplifiers have been realized with feedback mechanisms 3, 4, by combining magnetic tunnel junctions (MTJs) with electrically isolated metallic wires in a scheme known as spin transistor 5 or exciting MTJ resonance with a microwave field 6. The concept of microwave amplification based on spin-transfer torque in a three-terminal device was proposed by Slonczewski in one of his patents 2. Amplifiers serve as key elements in radio frequency circuits, however, with spintronic technology still in its infancy, no clear strategy for the development of spintronic amplifiers has emerged. ![]() Such a technology has the potential to impact the design of radio-frequency and microwave devices, improving their performance in terms of power consumption and compactness 1. The discovery of the giant-magnetoresistive effect and spin-transfer torque enabled the birth of spintronics, allowing devices to take advantage of the spin together with charge. ![]() Our work provides a way to develop a class of compact amplifiers that can impact the design of the next generation of spintronics-CMOS hybrid systems. Based on micromagnetic simulations and experiments, we describe the fundamental aspects driving the amplification and show the key role of the co-existence in microwave emissions of a dynamic state of the MTJ excited by a dc current and the injection locking mode driven by the microwave input signal. We achieve a record gain (| S 11 | > 2) for input power on the order of nW (<−40 dBm) at an appropriate choice of the bias field direction and amplitude. Here, we demonstrate a spintronic amplifier based on two-terminal magnetic tunnel junctions (MTJs) produced with CMOS-compatible material stacks that have already been used for spin-transfer torque memories. However, only a few concepts for spintronic amplifiers have been proposed, typically requiring complex device configurations or material stacks. Spintronics-based microwave devices, such as oscillators and detectors, have been the subject of intensive investigation in recent years owing to the potential reductions in size and power consumption.
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