Nb trilayer process has been serving as the most stable fabrication process of the Josephson junction integrated circuits for more than two decades. Fast development of semiconductor fabrication technology has been possible with the recent advancement of the fabrication equipment. In this work, we took an advantage of those advanced fabrication equipments in developing a superconducting arithmetic logic unit (ALU) by using Nb trilayers. We used DC magnetron sputtering technique for metal depositions and RF sputtering technique for SiO2depositions. Various dry etching techniques were used to define Josephson junction areas and various patterns of metallic and insulating layers. Our Nb films were stress-free and had the Tc's above 9 K. To enhance the step coverage of Nb films we used reverse bias DC magnetron sputtering technique. The fabricated 1-bit, 2-bit, and 4-bit ALU circuits were tested at a few kilo-hertz clock frequency as well as a few tens gigahertz clock frequency. Our 1-bit ALU operated correctly at up to 40 GHz clock frequency, and the 4-bit ALU operated at 5 GHz clock frequency.
Nb trilayer process has been serving as the most stable fabrication process of the Josephson junction integrated circuits for more than two decades. Fast development of semiconductor fabrication technology has been possible with the recent advancement of the fabrication equipment. In this work, we took an advantage of those advanced fabrication equipments in developing a superconducting arithmetic logic unit (ALU) by using Nb trilayers. We used DC magnetron sputtering technique for metal depositions and RF sputtering technique for SiO2depositions. Various dry etching techniques were used to define Josephson junction areas and various patterns of metallic and insulating layers. Our Nb films were stress-free and had the Tc's above 9 K. To enhance the step coverage of Nb films we used reverse bias DC magnetron sputtering technique. The fabricated 1-bit, 2-bit, and 4-bit ALU circuits were tested at a few kilo-hertz clock frequency as well as a few tens gigahertz clock frequency. Our 1-bit ALU operated correctly at up to 40 GHz clock frequency, and the 4-bit ALU operated at 5 GHz clock frequency.
We present a 4-bit Arithmetic Logic Unit (ALU) utilizing superconductor technology. The ALU serves as the central processing unit of a processor, performing crucial arithmetic and logical operations. We have adopted a bit-parallel architecture to ensure an efficient and streamlined design with minimal fanin/fanout and optimal latency. In terms of fabrication, the ALU has been fabricated using a standard commercial process. It operates at an impressive clock frequency exceeding 30 GHz while consuming a mere 4.75 mW of power, including applied reverse current, encompassing static and dynamic components. The ALU contains over 9000 Josephson junctions, with approximately 7000 JJs dedicated to wiring, delay lines, and path balancing, and it has over 18% bias margin. Designed as a co-processor, this arithmetic logic unit will work with external CMOS memory and processors via interface circuits. Thorough testing and validation of the ALU's functionality have been conducted with digital and analog simulations, and all the components were fabricated and measured within a 4K pulse-tube cryocooler. Experimental verification has confirmed the successful operation of both the arithmetic and logic units. These results have been analyzed and are presented alongside the experimental data to provide comprehensive insights into the ALU's behavior and capabilities.
We have designed, fabricated, and tested a rapid single flux quantum (RSFQ) 1 bit arithmetic logic unit (ALU) block. The circuit consists of three DC current driven SFQ switches and a half-adder. We successfully tested the half-adder cell at clock frequency up to 20 GHz. The switches were commutating output ports of the half-adder to produce AND, OR, XOR, or ADD functions. For a high-speed test, we attached two switches at the input ports of the half-adder to control the high-speed input data by low-frequency pattern generators. The output in this measurement was an eye-diagram. Using this set-up, the circuit was successfully tested up to 20 GHz. The chip was fabricated using a standard HYPRES 1 kA cm −2 Nb Josephson junction fabrication process.
As part of the effort to develop a superconductive microprocessor, we constructed a rapid single flux quantum (RSFQ) 4-bit arithmetic and logic unit (ALU) in a pipelined structure. To speed up the circuit, we used a forward clocking scheme. The 4-bit ALU consisted of ten RSFQ Half Adders, four 2 /spl times/ 2 switches, and several D flip-flops. By commutating output ports of the half adder, we were able to produce AND, OR, XOR, and ADD functions. The 4-bit ALU was fabricated using the Korea Photonics Technology Institute's ten-level 1.0 kA/cm/sup 2/ Nb process. The size of the ALU was 3.0 mm /spl times/ 1.5 mm, fitting in a 5 mm /spl times/ 5 mm chip. The fabricated 1-bit ALU block was successfully tested at up to a 40 GHz clock frequency. The complete 4-bit ALU operated correctly at up to a 5 GHz clock frequency.
• A high performance ALU is critical for overall processor performance. • Bypass technology reduces calculation time and prevents data hazards. • Carry-control optimization technology needs minimal hardware costs. • The ALU can perform all operations, achieving up to 100 % utilization. Two optimization technologies, namely, bypass and carry-control optimization, were demonstrated for enhancing the performance of a bit-slice Arithmetic Logic Unit (ALU) in 2 n -bit Rapid Single-Flux-Quantum (RSFQ) microprocessors. These technologies can not only shorten the calculation time but also solve data hazards. Among them, the proposed bypass technology is applicable to any 2 n -bit ALU, whether it is bit-serial, bit-slice or bit-parallel. The high performance bit-slice ALU was implemented using the 6 k A/cm 2 Nb/AlO x /Nb junction fabrication process from Superconducting Electronics Facility of Shanghai Institute of Microsystem and Information Technology. It consists of 1693 Josephson junctions with an area of 2.46 × 0.81 mm 2 . All ALU operations of the MIPS32 instruction set are implemented, including two extended instructions, i.e., addition with carry (ADDC) and subtraction with borrow (SUBB). All the ALU operations were successfully obtained in SFQ testing based on OCTOPUX and the measured DC bias current margin can reach 86 % - 104 % . The ALU achieves a 100 % utilization rate, regardless of carry/borrow read-after-write correlations between instructions.
In order to develop superconducting Digital Signal Processors (DSP's), we have been studying a superconducting 1-bit Arithmetic Logic Unit (ALU). This ALU has the simplest function of AND, OR, ADD (addition), and SUB (subtraction). The ALU operates in a 3-stage pipeline. All logic functions such as AND, OR, and SUM (summation) can be executed within a single stage of the pipeline. In order to achieve the high-speed operation of the ALU, we proposed and designed a novel 3-input XOR gate, which can operate in only one logic stage. Our simulation study showed that all components of the ALU can operate up to 50 GHz. These ALU components were fabricated and tested at low speed. Large bias margins of more than /spl plusmn/37% were achieved. The designed ALU's were laid out and fabricated with an Nb process. The ALU occupied the area of 1200 /spl mu/m /spl times/ 2600 /spl mu/m, which contains 560 Josephson junctions (JJ's).
We have developed a fabrication technology for superconducting integrated circuits with Nb-based Josephson junctions. The standard fabrication process with 10 mask levels includes 3 Nb superconducting layers and a Mo resistor layer. The influence of deposition parameters on film stress, electrical properties, and surface roughness were studied systematically. High quality Nb, Al, Mo, and SiO2films were successfully deposited for the subsequent fabrication of circuits. The circuit fabrication started with the fabrication of Mo resistors with a target sheet resistanceRshof 2 Ω, followed by the deposition of Nb/Al-AlOx/Nb trilayer Josephson-junction. The target critical current densityJcwas set at 6 kA/cm2. Small-scale circuits such as our standard library cells have been successfully fabricated and tested, confirming the capability of our fabrication technology for superconducting integrated circuits.