Abstract:We have found a memristive characteristic of an amorphous Ga-Sn-O (α-GTO) thin-film device with double layers of different oxygen density. The double layers are deposited using radio frequency (RF) magnetron sputtering, whose gas for the lower layer contains less oxygen, whereas that for the upper layer contains more oxygen, and it is assumed that the former contains more oxygen vacancies, whereas the latter contains fewer vacancies. The characteristic is explained by drift of oxygen and is stable without form… Show more
“…It is found that the oxygen concentration in the upper layer is higher than that in the lower layer. It has been also known that the oxygen concentration in the GTO thin film is surely dependent on the oxygen concentration in the sputtering gas 18 . Figure 2 Cross-sectional image ( a ) TEM image.…”
Artificial intelligence is a promising concept in modern and future societies. Presently, software programs are used but with a bulky computer size and large power consumption. Conversely, hardware systems named neuromorphic systems are suggested, with a compact computer size and low power consumption. An important factor is the number of processing elements that can be integrated. In the present study, three decisive technologies are proposed: (1) amorphous metal oxide semiconductor thin films, one of which, Ga–Sn–O (GTO) thin film, is used. GTO thin film does not contain rare metals and can be deposited by a simple process at room temperature. Here, oxygen-poor and oxygen-rich layers are stacked. GTO memristors are formed at cross points in a crossbar array; (2) analog memristor, in which, continuous and infinite information can be memorized in a single device. Here, the electrical conductance gradually changes when a voltage is applied to the GTO memristor. This is the effect of the drift and diffusion of the oxygen vacancies (Vo); and (3) autonomous local learning, i.e., extra control circuits are not required since a single device autonomously modifies its own electrical characteristic. Finally, a neuromorphic system is assembled using the abovementioned three technologies. The function of the letter recognition is confirmed, which can be regarded as an associative memory, a typical artificial intelligence application.
“…It is found that the oxygen concentration in the upper layer is higher than that in the lower layer. It has been also known that the oxygen concentration in the GTO thin film is surely dependent on the oxygen concentration in the sputtering gas 18 . Figure 2 Cross-sectional image ( a ) TEM image.…”
Artificial intelligence is a promising concept in modern and future societies. Presently, software programs are used but with a bulky computer size and large power consumption. Conversely, hardware systems named neuromorphic systems are suggested, with a compact computer size and low power consumption. An important factor is the number of processing elements that can be integrated. In the present study, three decisive technologies are proposed: (1) amorphous metal oxide semiconductor thin films, one of which, Ga–Sn–O (GTO) thin film, is used. GTO thin film does not contain rare metals and can be deposited by a simple process at room temperature. Here, oxygen-poor and oxygen-rich layers are stacked. GTO memristors are formed at cross points in a crossbar array; (2) analog memristor, in which, continuous and infinite information can be memorized in a single device. Here, the electrical conductance gradually changes when a voltage is applied to the GTO memristor. This is the effect of the drift and diffusion of the oxygen vacancies (Vo); and (3) autonomous local learning, i.e., extra control circuits are not required since a single device autonomously modifies its own electrical characteristic. Finally, a neuromorphic system is assembled using the abovementioned three technologies. The function of the letter recognition is confirmed, which can be regarded as an associative memory, a typical artificial intelligence application.
“…technologies [13,14]. On the other hand, amorphous metal-oxide semiconductor (AOS) thin films are being investigated for diverse applications [15][16][17][18][19][20][21][22][23][24][25][26][27] and proposed also for neuromorphic systems [28][29][30][31][32][33][34][35][36][37][38], whose advantages are that they have analog characteristic [39] and can have three-dimensional structure [40].…”
A multilayer crossbar array has been developed using amorphous metal-oxide semiconductor (AOS) thin films and implemented into a neuromorphic system. The multilayer structure can be realized, because the AOS thin films can be deposited by a simple sputtering method without heat treatment, which does not damage the underlying structures. First, Au thin films are deposited by vapor evaporation as electrodes, an amorphous In-Ga-Zn-O (-IGZO) thin film is deposited by a sputtering method as a conductance change layer, these processes are repeated, and a multilayer crossbar array is completed, where each of the three conductance change layers is sandwiched between the electrodes. Next, the multilayer crossbar array is implemented into a neuromorphic system with modified Hebbian learning, which enables autonomous learning without control circuitry, and an associative memory function is confirmed, which guarantees the possibility of further advanced functions. These results lead to astronomical large-scale integration (LSI) of synaptic elements in neuromorphic systems in the future.
“…On the other hand, we are investigating one of the AOS devices [6], Ga-Sn-O (GTO) devices, because they do not include rare and toxic metals such as In [7]. Moreover, we are developing GTO thin-film memristors and other metal-oxide semiconductor synapse elements [8][9][10][11][12][13][14]. Of course, other research institutes are also developing memristors of various materials as synapse elements [15][16][17][18][19][20][21][22][23].…”
Ga-Sn-O (GTO) thin-film memristor has been developed, and an analog plasticity characteristic has been observed. First, GTO thin-film memristors are fabricated by depositing three GTO layers in a stacked structure using sputtering. Next, the current-voltage characteristics are measured by varying the maximum applied voltage after a certain negative voltage, the hysteresis is observed, and the switching characteristics are evaluated, which is regarded as that an analog plasticity characteristic is observed. The parametric study is done for the stacked structure and deposition process, and the proposed operating mechanism is that oxygen vacancies reciprocate by applying negative and positive voltages. Finally, the pulse application characteristic shows the long-term potentiation and depression, which presents a practical possibility to utilize the GTO thin-film memristor for neuromorphic systems.
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