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We describe uncooled infrared focal plane arrays (IRFPAs), which consist of pn junction diodes fabricated on a silicon-on-insulator (SOI) layer using a complementary metal oxide semiconductor (CMOS) process. Based on this technique, we released the Mitsubishi Electric Diode Infrared sensor (MelDIR) into the thermal detector market in 2019. This sensor is an 80×32 IRFPA with a 25 μm pixel pitch, utilizing a chip-scale vacuum-packaging process. To reduce the sensor cost, we developed a common differential circuit that switches the column pixel line, and achieved a significant reduction in chip area. In order to use a low-cost lens in the sensor module, we also developed an aberration correction method that improves the temperature measurement accuracy. Furthermore, we evaluated the effectiveness of a shutter-less method based simply on the thermal behavior of the SOI diode. These techniques allow enhanced performance of the MelDIR.

We developed silicon-on-insulator (SOI) diode-based uncooled infrared focal plane arrays (IRFPAs), in which single-crystal pn junction diodes formed in an SOI layer are used as temperature sensors. These diodes, based on silicon large-scale integration technology, offer excellent uniformity, and have led to the use of high-performance uncooled IRFPAs in a wide variety of applications. In order to extend the pitch to less than 12 μm, a scalable new pixel structure has been developed to reduce the pixel size, based on a novel thermally isolated structure, which is fabricated above a CMOS processed wafer. The pn junction diodes used as a temperature sensor are separated from the underlying substrate by supporting legs made from thin metal wire, forming a cavity. To reduce the pixel size, we are developing a new diode structure by optimizing the ion implantation condition, thinning the SOI layer, and redesigning the supporting legs, achieving a smaller pixel size even with ten serially connected diodes. We also evaluated a new readout circuit architecture that enables an increase in sensitivity by generating a larger change in the diode forward voltage at a given temperature with no change in the number of diodes in the SOI layer. The effectiveness of the proposed readout circuit architecture was verified using a fabricated test element. The sensitivity of the test element was 128% of that for existing circuit structures, and further increases are expected with circuit structure optimization. These techniques have greatly enhanced the performance of our SOI diode based uncooled IRFPAs.

In this study, we develop a shutter-less algorithm for a silicon-on-insulator (SOI) diode uncooled infrared focal plane array (IRFPA). The optimal non-uniformity correction is calculated onboard. The effectiveness of the proposed algorithm was verified using a prototype uncooled IR camera. The performance of the shutter-less algorithm was studied by measuring a fixed pattern noise (FPN) at different correction points and verification of favorable camera operation. Even at two correction points, the FPN was at a practical level. The temperature behavior of the proposed SOI diode is highly uniform and predictable, which leads to simpler device modeling and therefore simpler shutter-less operation. A new pixel structure was also developed for pixel size reduction. This approach is based on the realization of a novel thermal isolation structure that can be fabricated by post processing on top of CMOS wafers. Ten series diodes can be arranged in a pixel by designing a 12 μm pixel pitch IRFPA with the new pixel structure. These developed technologies have significantly enhanced the performance of the SOI diode uncooled IRFPA, which inherently possesses excellent uniformity and low noise.

We develop a shutter-less method for replacing mechanical shutters. To verify the effectiveness of the proposed method, we fabricated a silicon-on-insulator (SOI) diode uncooled 320 × 240 infrared focal plane array (IRFPA) with 17 μm pixel pitch utilizing a circuit architecture that achieves thermo-electric cooling (TEC)-less operation. Furthermore, we fabricated a prototype uncooled IR camera that implements the proposed method and verified favorable camera operation. The temperature behavior of our proposed SOI diode is highly uniform and predictable, which enables simpler device modeling and consequently simpler TEC-less and shutter-less operation.

We found that the offset field (H off ) of a top-pinned magnetic tunnel junction (MTJ) with a CoPd/Ru/Ta/CoFeB-synthetic antiferromagnetic (SAF) free layer can be reduced by controlling the exchange coupling energy (J ex ) value. A micromagnetic simulation was used to derive the direct relation between the J ex ) of a CoPd/Ru/Ta/CoFeB-SAF free layer and the H off ) of a top-pinned MTJ with the SAF free layer. In addition, we found that the J ex ) value can be controlled by changing the thickness of the Ta spacer between the CoPd and CoFeB layers. As a result, we fabricated a top-pinned MTJ with a SAF free layer that eliminated the offset field and made it possible to improve the thermal stability.

Synthetic antiferromagnetic (SAF) free layers consisting of [Co (0.3 nm)/Pd (0.7 nm)]n/Ru/Ta/CoFeB were investigated for use in the free layers of top-pinned magnetic tunnel junctions (MTJs). We found that interlayer exchange coupling properly provides thermal stability when the saturation magnetization of the CoPd layer is less than that of the CoFeB layer. Furthermore, we demonstrated that the thermal stability factor of the top-pinned MTJ with [Co (0.3 nm)/Pd (0.7 nm)]n=1/ Co (0.3 nm)/Ru/Ta/CoFeB- SAF free layers was improved without increasing the intrinsic switching current.

We applied Co20Fe60B20 layers with thicknesses from 1.2 to 1.5 nm to the sensing layers of MgO based magnetic tunnel junctions (MTJs) with spin-valve-type structures annealed at 350 °C for magnetic field sensors. The CoFeB layer on MgO had in-plane magnetic anisotropy and also slight perpendicular magnetic anisotropy that originated at the MgO/CoFeB interface. MR characteristics of high reversibility and linearity were confirmed at a CoFeB thickness of 1.3 nm. We consider that the hysteresis-free properties of the sensing layer were obtained by the balance between in-plane magnetization and other components in magnetization including out-of-plane magnetization.

Ni–Fe/Mn–Ir asymmetric ring dots with partially planed outer sides are investigated in order to confirm a method for obtaining pinned layers in magnetic memories with asymmetric ring shapes. Magnetic force microscopy revealed that the direction of vortical magnetization is pinned in Ni–Fe/Mn–Ir asymmetric ring dots despite the direction of the magnetic fields. This investigation shows that the Ni–Fe/Mn–Ir asymmetric ring dots can be applied to pinned layers in magnetic memories with asymmetric ring shapes.

We have investigated (Ba,Sr)TiO 3 (BST) films grown on Ru by a liquid source chemical vapor deposition (CVD). Inductively coupled plasma mass spectrometry (ICP-MS) analysis revealed the decline of (Ba+Sr)/Ti molar ratio of the initial BST-layer on Ru. By readjusting the flow ratio of the liquid sources and using a two-step deposition method, we obtained 30-nm-thick BST films with a uniform composition profile and exhibiting good electrical properties. The leakage property, however, was severely deteriorated in BST films less than 24 nm thick. Scanning electron microscopy observation showed the presence of micro-roughness or micro-hillocks in these films. An annealing process of the Ru electrode was added for its planarization, and the CVD process was also improved to suppress oxidation of Ru. As a result, we obtained smooth and finely crystallized ∼20-nm-thick BST films with good electrical properties at an equivalent SiO 2 thickness ( t eq ) of ∼0.45 nm and leakage current −7 A/cm 2 . We also measured the properties of BST films deposited on the three-dimensional Ru electrode.

Ni–Fe asymmetric ring dots with partially planed outer sides were investigated as candidates for high-density magnetic memory cells. The magnetic states, which were measured with magnetic force microscopy, show that in-plane magnetic fields can control the chirality, either clockwise or counterclockwise, of vortical magnetizations of the Ni–Fe asymmetric ring dots. This control facilitates applying ring dots to the magnetic random access memories.

We have experimentally investigated a method of controlling the magnetization direction of a CoFe pinned layer in a spin-valve-type magnetic tunnel junction (MTJ) with an IrMn layer. Arbitrary control of the direction of the pinned layer magnetization was performed by a postannealing process in conditions above the blocking temperature of IrMn and in a magnetic field to saturate the magnetization of the pinned layer. The results show that it is possible to control and to uniformly rearrange the direction of the pinned layer magnetization in MTJs with a postannealing process in the magnetic random access memories manufacturing process.

We evaluated MgO-based magnetic tunnel junctions (MTJs) for magnetic field sensors with spin-valve-type structures in the CoFeB sensing layer capped by an MgO film in order to obtain both top and bottom interfaces of MgO/CoFeB exhibiting interfacial perpendicular magnetic anisotropy (PMA). Hysteresis of the CoFeB sensing layer in these MTJs annealed at 275 °C was suppressed at a thickness of the sensing layer below 1.2 nm by interfacial PMA. We confirmed that the CoFeB sensing layers capped with MgO suppress the thickness dependences of both the magnetoresistance ratio and the magnetic behaviors of the CoFeB sensing layer more than that of the MTJ with a Ta capping layer. MgO-based MTJs with MgO capping layers can improve the controllability of the characteristics for magnetic field sensors.

We investigated the exchange-coupling fields of CoFe/Ru (tRu)/CoFe synthetic antiferromagnetic (SyAF) structures with a Ru underlayer and capping layer before and after annealing at 300 and 350 °C. Exchange-coupling field Hex decreased after annealing and distribution increases in Hex were observed in the structure of smaller tRu, especially at tRu≤0.7 nm. Remanence magnetizations increased at smaller tRu. These results indicate that distribution is caused by the existence of the antiferromagnetic coupling of locally various coupling fields due to annealing. A larger exchange-coupling field after high temperature annealing can be obtained by suppressing the distribution of the exchange coupling in the SyAF structure.

We have investigated the magnetic switching properties of synthetic antiferromagnetic (SyAF) structures consisting of Co90Fe10∕Ru∕Co90Re10 structure with a Ru capping layer annealed at 300°C. After annealing, the coercivity Hc of the structures with a Co90Fe10 thickness below 5nm increased. On the other hand, the Hc was maintained below 70Oe in structures with a Co90Fe10 thickness above 6nm after annealing. Thus, a low switching field for a free layer can be achieved by using the SyAF structures with a Ru capping layer, even after annealing at 300°C, and the SyAF free layer is considered to be effective for downsized memory cells in magnetic random access memories.

The transition between onion states and vortex states in exchange-coupled Ni–Fe∕Mn–Ir asymmetric ring dots has been investigated. A direction of domain wall motion, during the transition from the single-domain state to the vortex state via the onion state, depends on a sweep direction of an external field. This dependence fixes the directions of vortical magnetizations in the vortex states. The derivative of the amount of the domain wall motion with respect to the external field depends on the sweep direction of external field, and thus the hysteresis loop becomes asymmetric.

Experimental studies of the etching of (Ba,Sr)TiO3 (BST) have been performed in Ar/halogen and Cl2 plasmas. In spite of the poor volatility of halogenated barium and strontium, some chemical enhancement of the etching reaction was observed in the etching of BST with halogen-containing plasmas. An investigation of the etching of BaOx, SrOx, TiOx, and BaxSryOz films with Cl2 plasma showed that the chemical enhancement in BST etching was related to the existence of titanium in BST films. The chemical reactivity of titanium with chlorine seemed to enhance the etching of BST. In the x-ray photoelectron spectroscopy analysis of the BST surfaces etched with Cl2 plasma, we found that barium- and strontium-rich surfaces were formed during the etching and that etching residues consisting of barium and strontium were observed after the BST films were etched off.