Osamu Hidaka

Ferroelectric Properties of Pb(Zi, Ti)O3 Capacitor with Thin SrRuO3 Films within Both Electrodes.

Ferroelectric properties of a Pb(Zi, Ti)O3 (PZT) capacitor with thin SrRuO3(SRO) films within both electrodes were investigated in detail. Thin SRO films of 10 nm thickness markedly improve the electrical performance, such as switching charge (Qsw), saturation characteristics of the hysteresis curve and imprint performance even at an elevated temperature. It should also be noted that there was no Qsw degradation after 5×1010 read/write cycles at 5 V. No leakage current increase after the test was observed. The results of transmission electron microscope (TEM) and electron dispersive X-ray (EDX) analyses also showed that there is no diffusion of either Sr or Ru in the PZT film. The Qsw increase can be explained by the model in which excess oxygen ions existing in the SRO films drift into the PZT due to the external electric field where they fill the oxygen vacancies in the PZT near the interfaces. We confirmed that the proposed electrode structure was a key to realizing highly reliable ferroelectric random access memories (FRAMs).

Precise extraction of emitter resistance from an improved floating collector measurement

A distributed transistor model is developed which comprehensively explains the non-linear characteristics of floating collector measurements. The non-linearity is attributed to the fact that the intrinsic collector current is not zero when the collector terminal is opened. Based on this understanding, a new procedure to extract emitter resistance is proposed. Combining the measurements of forward and reverse current gains and intrinsic base sheet resistance, the ambiguity in the conventional floating collector measurement is diminished and hence the accuracy is significantly improved. >

Thermal Runaway Tolerance in Double-Heterojunction Bipolar Transistors

On the double-heterojunction bipolar transistor (DHBT) with a narrow band-gap base, collector current is strongly impeded at a high current level where the base-pushout effect occurs. This phenomenon was studied in conjunction with the thermal stability of transistors. The experimental comparison of Si/SiGe/Si-DHBT with a Si bipolar junction transistor (Si-BJT) confirmed that SiGe-DHBTs are more stable with regard to thermal runaway than Si-BJTs.