Kazuo Tsubouchi

Fabrication of 5-GHz-band SAW filter with atomically-flat-surface AlN on sapphire

5-GHz-band surface acoustic wave (SAW) filters for mobile communications were fabricated on an atomically-flat-surface (0001)aluminum nitride/(0001)sapphire (AlN/Al/sub 2/O/sub 3/) combination. The SAW devices were fabricated using electron beam lithography and a lift-off method. Atomically-flat-surface AIN films were used to reduce SAW propagation loss. The center frequency of the fabricated SAW filter was 5.18 GHz. SAW velocity was 5688 m/s at normalized thickness by wave number (kH) of 9.9. The effective coupling coefficient was 0.1% and temperature-coefficient of delay was 9 ppm//spl deg/C at kH of 5.9. The SAW propagation loss was 0.0053 dB at 5.18 GHz. The atomically-flat-surface (0001)AlN/(0001)Al/sub 2/O/sub 3/ combination is promising for use in 5-GHz-band SAW filters for application to mobile communications.

Surface Acoustic Wave Properties of Atomically Flat-Surface Aluminum Nitride Epitaxial Film on Sapphire

We have investigated the surface acoustic wave (SAW) properties of atomically flat-surface (0001)aluminum nitride on a (0001)sapphire (AlN/α-Al2O3) combination. SAW propagated along [1210]AlN/[1100]α-Al2O3 and [1010]AlN/[1120]α-Al2O3. SAW velocity was measured to be approximately 1.0% higher than that of a conventionally calculated curve. The dispersion of SAW velocity as a function of normalized thickness (kH) was as low as 1.3%. The measured temperature coefficient of delay was 9 ppm/°C at kH values of 5.9 and 9.9. The propagation loss in the case of using an atomically flat-surface AlN film was lower by one order of magnitude than that using a conventional AlN film. The propagation loss at 5.172 GHz was measured to be 0.0053 dB/λ.

Growth of atomically flat-surface aluminum nitride epitaxial film by metalorganic chemical vapor deposition

A high c-axis-oriented and atomically flat-surface aluminum nitride (AlN) film has been successfully deposited on a (0001)sapphire substrate by metalorganic chemical vapor deposition. We evaluated the dependences of surface roughness, tilted mosaicity and twisted mosaicity on the conditions of AlN deposition. It was found that the atomically flat-surface AlN film was deposited under the diffusion-limited area with suppression of vapor phase reaction at a substrate temperature of 1200°C and a V/III ratio of 800. It was also recognized that surface roughness was controlled by gas flow velocity, which is determined by both gas flow rate and pressure in reactor. Mean surface roughness (Ra) of the deposited AlN films was approximately 1 A. The full width at half maximum of X-ray rocking curve for (0002) and (1012)AlN were approximately 100 and 2300 arcsec, respectively.

New current attenuator circuit in the current mode FFT LSI for OFDM

To achieve the high performance of current-mode fast-Fourier-transform (FFT) large-scaled integration (LSI) for orthogonal frequency division multiplexing (OFDM) system, a new current-attenuator circuit without a DC offset-current error is proposed. The attainable maximum scale accuracy to the input current is theoretically -80 dB in the proposed attenuator circuit. The circuit consists of N-current mirrors simply connected in parallel with one another. The output current of the circuit is reduced to 1/N of the input current. The proposed circuit exerts high accuracy on the current attenuation and enables us to design the current-mode 64-point FFT LSI for OFDM system.

Switched-Current Analog Programmable Filter for Software-Defined Radio

We have proposed a switched-current (SI) analog programmable finite-impulse-response (FIR) filter for software-defined radio. The programmable tap coefficient circuit for programmable operation of the SI FIR filter has also been proposed. The 4-bit-resolution tap coefficient circuit has been designed and fabricated using 0.35 µm complementary-metal-oxide-semiconductor technology. The current error between measured and calculated tap coefficient circuits has been less than 2%. The radio frequency/intermediate frequency SI band-pass filter has been designed using the measured tap coefficients. The designed SI FIR filter has a frequency response as well as calculated tap coefficients. The maximum operating frequency of the proposed SI FIR filter using 0.13 µm CMOS technology has been estimated to be greater than 10 GHz with circuit simulation.

Voltage to current converter for OFDM current-mode FFT LSI

We have implemented a low power current-mode fast Fourier transform (FFT) large-scale integration (LSI) for orthogonal frequency division multiplexing (OFDM) system. In this paper, a new voltage-to-current converter (VIC) with high f?equency operation and low power consumption is proposed. From the VIC measurement result, the power consumption was 440 pW at Vdd = 1.1 V and the operating frequency amounted to 226.26 MHz.

Lower Boundary of Supply Voltage in Digital ULSI Based on the Communication Theory

We have proposed a theoretical design method for the lower boundary of supply voltage using the universal Eb/N0-bit error rate (BER) characteristics from the system viewpoint. In order to achieve the system error rate of less than 10-10 with the conditions of 10 years term, 10 GHz clock and 106 gate, the bit error rate of a gate should be less than 10-34. For a BER of 10-34, VDD should be larger than 0.1 V for 0.13 µm complementally metal-oxide-silicon (CMOS) LSI. For 0.05 µm CMOS of next generation, VDD should be larger than 0.2 V under the ideal thermal noise environment. The measured Eb/N0-BER characteristics of CMOS circuits as a function of supply voltage have agree well with the theoretical value.