Kazuhiro Baba

Early formation of chemical vapor deposition diamond films

Nanometer‐size diamond particles formed on a silicon substrate by the hot‐filament chemical vapor deposition method were examined by a high‐resolution electron microscope. The particles developed well‐faceted cuboctahedral habits. Examination of their morphologies and microstructures provides a wealth of information on their crystal growth mechanism. The effect of the pretreatment of the substrate by diamond powder, which has been known to enhance thin‐film growth, was found to be due to seeding by ‘‘diamond dust’’ on the substrate surface.

Growth of diamond particles in chemical vapor deposition

An early stage of diamond growth in hot-filament chemical vapor deposition on silicon substrates was examined by the high resolution electron microscope. “Pretreatment” of the substrate surfaces by diamond powder abrading was found to plant diamond seed crystals with a density of as high as 10 11 /cm 2 . These crystals provide sites for subsequent growth of diamond films. The CVD grown diamond particles tend to be cuboctahedra. Smaller particles in nanometer size are faultless, but larger ones of several tens of nanometers develop crystal faults. Some of them may originate from the seed crystals. Degradation of the diamond seed crystals due to the electron beam irradiation is discussed in terms of fabrication of diamond film.

Synthesis and properties of ultrafine AlN powder by rf plasma

High‐purity ultrafine AlN powder was synthesized by rf plasma through direct nitridation of Al. The specific surface area was about 30 m2 /g under typical experimental conditions. Ultrafine AlN powder showed excellent sinterability, compared with conventional AlN powders, whose particle sizes were more than 0.5 μm. The thermal conductivity for the sintered body reached 220 W/m K when sintered at 1900 °C, and 110 W/m K when sintered at 1400 °C, by using YF3 as a sintering aid.

Thermal conductivity of diamond films

The thermal diffusivity of diamond films grown on the Si substrate by the hot‐filament chemical vapor deposition technique in gas mixtures of 1% to 5% methane in hydrogen were studied. Thermal conductivity of the film prepared at 1% CH4 concentration reached about 1200W/mK, which is almost equal to that for type I natural diamond, and decreased rapidly to less than 200W/mK with increasing CH4 concentration. Hydrogen contents in the films increased with a decrease in thermal conductivity. This indicates that the thermal conductivity for diamond films is correlated to the amount of incorporated hydrogen impurity.

The grain size dependence of the mobility and lifetime in chemical vapor deposited diamond photoconductive switches

The grain size dependence of the carrier lifetimes and collection distances of chemical vapor deposited (CVD) diamond films of 0.1–10 μm average grain size was measured. The estimated values of the mobilities and lifetimes indicated that the dominant recombination process had occurred inside the grains, not the grain boundaries. This finding was confirmed by measuring the electric field dependence of the lifetime and the collection distance. Under a high electric field, however, a major decrease in decay time is expected for smaller grain sizes, due to the increase in the number of carriers which reach the grain boundaries during their lifetime. Such a decrease was observed in a 0.8-μm grain size sample at E=105 V/cm. The data also showed that a 1-ps kV electrical pulse from a dc bias across a diamond film coated gap can be achieved with a CVD-deposited diamond photoconductive switch of sub-μm grain size.

Photoconductive properties of chemical vapor deposited diamond switch under high electric field strength

Photoconductive properties of diamond optical switch made by chemical vapor deposition method were investigated. A new configuration of the diamond gap was proposed to reduce the surface leakage current and avoid surface flashover. This technology made it possible to apply static high electric field up to 2×106 V/cm. The dependence of the mobility‐lifetime product (μτ) on the grain size was measured for a wide range of electric field. The μτ value was increased to be linearly proportional to the electric field for every grain size sample, and no saturation was measured even at a high electric field of E=3×105 V/cm. Larger grain size samples had larger μτ values. The grain size dependence was attributed to the decreasing of the mobility or the lifetime inside the grain not due to the increasing recombination ratio at the grain boundary in smaller grain size samples.

Low-impedance evaluation of power distribution network for decoupling capacitor embedded interposers of 3-D integrated LSI system

We evaluated low-impedance power distribution network (PDN) of decoupling capacitor embedded interposers for 3-D integrated LSI system. Measurements are carried out using the developed impedance analyzer system of a wide frequency range for evaluating ultralow impedance, and calculations are carried out using 2.5-D finite element method (FEM) electromagnetic field simulator. We fabricated various types of capacitor mounted or capacitor embedded interposers test element group (TEG), such as surface-mounted and embedded chip capacitors, and thin film capacitors on silicon interposers using the same simple design to compare measurement results with calculation ones. As a result, the chip capacitor embedded organic interposer TEG and thin film capacitor embedded silicon interposer TEG could provide low PDN impedance at a wide frequency range of up to 40 GHz. In particular, the interposer TEGs of the thin film capacitor embedded interposer that shows a low impedance of 0.1 Ω could be evaluated and calculated accurately. By using chip capacitor embedded or thin film capacitor embedded interposers for 3-D integrated LSI system, it is expected that the PDN of the system can be achieved ultralow PDN impedance.

Mechanical properties of diamond membranes

Polycrystalline diamond films were deposited using the hot-filament chemical vapor deposition method. The fracture strength for these membranes was estimated in a bulge test and from Youngs modulus measurement. These mechanical properties are changed by the substrate pretreatment conditions, the methane concentration, and the dc bias application between filaments and substrate. The maximum fracture strength was achieved at 2200 MPa, when 700 mA dc bias current was applied. The main characteristics for this film are a small grain size (0.3 µm) with relatively low nondiamond carbon content. It is concluded that the mechanical properties for diamond film are greatly affected by both grain size and nondiamond content in the film.

3D stacked buck converter with 15μm thick spiral inductor on silicon interposer for fine-grain power-supply voltage control in SiP's

This paper proposes a 3D stacked buck converter with a 15μm thick spiral inductor on a silicon Interposer, which is suitable for fine-grain power-supply voltage control in SiPs. Our newly developed silicon interposer technology realizes a fine-pitch design rule (Line/Space=20μm/20μm, via hole diameter =30um) at the metal thickness of 15μm as well as conventional interposers with 5μm metal thickness. The measurement result shows that the 15μm thick inductor improves the power efficiency of the buck converter by 12% at the output current of 100mA compared with that by the conventional 5-μm thick inductor.

Microscale Wear Properties of Ultrathin Diamond-Like Carbon Films

Microscale wear properties of ultrathin diamond-like carbon (DLC) films grown by rf plasma-enhanced chemical vapor deposition were investigated using an atomic force microscope. It was revealed that a low wear-resistant layer, which contained a larger sp2 component, existed on the surface of the films. The thickness of the layer depended on the self-bias voltage during deposition. The intermixing of carbon and silicon atoms at the interface between the DLC and the substrate was found to affect the surface wear resistance of ultrathin DLC films.