Silicon germanium (SiGe) has moved from being a research material to accounting for a small but significant percentage of manufactured semiconductor devices. This percentage is predicted to increase substantially as SiGe begins to be used in complementary metal oxide semiconductor (CMOS) technology in the future to substantially improve performance. It is the development of Si/SiGe heterostructures which has enabled band structure and strain engineering allowing Si/SiGe to be used in many different ways to improve conventional microelectronic device performance along with allowing new concepts to be explored. This paper presents a review of the material properties, growth techniques, band structure and the main electronic devices of the Si/SiGe heterostructure system. In particular, the important device technologies in mainstream microelectronics of the SiGe heterostructure bipolar transistor (HBT) and strained-Si CMOS will be reviewed before future device and optoelectronics concepts are explored.

https://iopscience.iop.org/article/10.1088/0268-1242/19/10/R02/pdf

Si/SiGe heterostructures: from material and physics to devices and circuits

The resonant tunneling diode (RTD) has been widely studied because of its importance in the field of nanoelectronic science and technology and its potential applications in very high speed/functionality devices and circuits. Even though much progress has been made in this regard, additional work is needed to realize the full potential of RTD's. As research on RTD's continues, we will try in this tutorial review to provide the reader with an overall and succinct picture of where we stand in this exciting field or research and to address the following questions: What makes RTD's so attractive? To what extent can RTD's be modeled for design purposes? What are the required and achievable device properties in terms of digital logic applications? To address these issues, we review the device operational principles, various modeling approaches, and major device properties. Comparisons among the various RTD physical models and major features of RTD's, resonant interband tunneling diodes, and Esaki tunnel diodes are presented. The tutorial and analysis provided in this paper may help the reader in becoming familiar with current research efforts, as well as to examine the important aspects in further RTD developments and their circuit applications.

/pdf/resonant-tunneling-diodes-models-and-properties-16lzfs8v3d.pdf

Resonant tunneling diodes: models and properties

The combination of resonant-tunneling diodes and heterostructure field-effect transistors provides a versatile technology for implementing microwave digital and mixed-signal applications. Here we demonstrate and characterize the first monolithic flash analog-to-digital converter (ADC) in this technology. The first-pass ADC achieved 2.7 effective bits at 2 gigasamples per second (Gsps) for a 220-MHz input signal. The one-bit quantizer achieved a single-tone spurious free dynamic range greater than 40 dB at 2 Gsps for a 220-MHz single-tone input with dithering.

A monolithic 4-bit 2-Gsps resonant tunneling analog-to-digital converter

This paper describes a new high-density low-power circuit approach for implementing static random access memory (SRAM) using low current density resonant tunneling diodes (RTDs). After an overview of semiconductor random access memory architecture and technology, the concept of tunneling-based SRAM (TSRAM) is introduced. Experimental results for a compound semiconductor 1-bit 50-nW TSRAM gain cell using low current density (/spl sim/1 A/cm/sup 2/) RTDs and low-leakage heterostructure field effect transistors are presented. We describe a one-transistor TSRAM cell which could convert silicon dynamic RAM (DRAM) to ultradense SRAM if an ultralow current density (/spl sim/1 /spl mu/A/cm/sup 2/) silicon bistable device is developed. Finally, we present experimental and simulation results for a TSRAM cell using multipeaked I-V curve devices and a multivalued word line. This approach aims at increasing storage density through vertical integration of bistable devices such as RTD's.

Tunneling-based SRAM

Resonant interband tunneling diodes on silicon substrates are demonstrated using a Si/Si0.5Ge0.5/Si heterostructure grown by low temperature molecular beam epitaxy which utilized both a central intrinsic spacer and δ-doped injectors. A low substrate temperature of 370 °C was used during growth to ensure a high level of dopant incorporation. A B δ-doping spike lowered the barrier for holes to populate the quantum well at the valence band discontinuity, and an Sb δ-doping reduces the doping requirement of the n-type bulk Si by producing a deep n+ well. Samples studied from the as-grown wafers showed no evidence of negative differential resistance (NDR). The effect of postgrowth rapid thermal annealing temperature was studied on tunnel diode properties. Samples which underwent heat treatment at 700 and 800 °C for 1 min, in contrast, exhibited NDR behavior. The peak-to-valley current ratio (PVCR) and peak current density of the tunnel diodes were found to depend strongly on δ-doping placement and on the annea...

http://www2.ece.ohio-state.edu/~berger/papers/1998oct-apl-rommel.pdf

Room temperature operation of epitaxially grown Si/Si0.5Ge0.5/Si resonant interband tunneling diodes

A 50-nW standby power compound semiconductor tunneling-based static random access memory SRAM (TSRAM) cell is demonstrated by combining ultralow current-density resonant-tunneling diodes (RTDs) and heterostructure field-effect transistors (HFETs) in one integrated process on an InP substrate. This power represents over two orders of magnitude improvement over previous III-V static memory cells. By increasing the number of vertically integrated RTD's we obtain a 100 nW tri-state memory cell. The cell concept applies to any material system in which low current-density negative differential resistance devices are available.

RTD/HFET low standby power SRAM gain cell

The combination of resonant tunneling diodes (RTDs) and heterostructure field-effect transistors (HFETs) provides a versatile technology for implementing microwave digital and mixed-signal applications. Here we demonstrate the first monolithic flash RTD/HFET analog-to-digital converter (ADC). The first pass ADC achieved 2.7 effective bits at 2 GSps. The one bit quantizer achieved a single tone spurious free dynamic range (SFDR) of greater than 40 dB at 2 GSps for a 220 MHz single tone input with dithering.

Iii. E.A. Beam

Papers

RTD/HFET low standby power SRAM gain cell

A monolithic 4 bit 2 GSps resonant tunneling analog-to-digital converter