Si/SiGe resonant interband tunnel diode

A Si/SiGe resonant interband tunnel diode (RITD) is a type of resonant interband tunnel diodes which is based on Si/SiGe materials.

All types of tunnel diodes, including Si/SiGe resonant interband tunnel diodes, make use of the quantum mechanical tunneling effect. Characteristic to the current-voltage relationship of a tunnel diode is the presence of one or more negative differential resistance region, which enables many unique applications. Tunnel diodes are also capable of high speed operation because the quantum tunneling effect is a fast process.

Compared to the Esaki tunnel diodes, which are essentially discrete diodes and therefore incompatible with modern Si integrated circuit technologies, the Si/SiGe resonant interband tunnel diodes are such that their structure and fabrication are suitable for integration with modern Si complemenraty metal-oxide-semiconductor (CMOS) and Si/SiGe heterojunction bipolar technology.

Resonant tunnel diodes and resonant interband tunnel diodes were first realized in III-V compound material systems utilizing hetrojunctions made up of various III-V compound semiconductors. Reasonably high performance III-V resonant tunnel diodes have been realized. But such devices have not entered mainstream applications yet because the processing of III-V materials is incompatible with Si CMOS technology and the cost is high.

Si/SiGe resonant tunnel diodes suffer from limited performance because of the limited conduction band and valance band offsets.

Si/SiGe resonant interband tunnel diodes are developed ^[1], which offer the advantage of being compatible with the mainstream Si CMOS technology.

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Structure

The structure of a typical Si/SiGe resonant interband tunnel didoe is shown on the right. Also shown is the corresponding band diagram calculated by Gregory Snider's 1D Poisson/Schrodinger Solver.

The five key points to the design are: (i) an intrinsic tunneling barrier, (ii) delta-doped injectors, (iii) offset of the delta-doping planes from the heterojunction interfaces, (iv) low temperature molecular beam epitaxial growth (LTMBE), and (v) postgrowth rapid thermal annealing (RTA) for dopant activation and point defect reduction ^[1].

Performance

A minimum PVCR of about 3 is needed for typical circuit applications. Low current density Si/SiGe RITDs are suitable for low-power memory applications, and high current density tunndel diodes are needed for high speed digital/mixed-signal applications. Si/SiGe RITDs have been engineered to have room temperature PCVRs up to 4.0 ^[2]. The same structure was duplicated by another research group using a different MBE system, and PVCRs of up to 6.0 have been obtained ^[3]. In terms of peak current density, peak current densities ranging from as low as 20 mA/cm² and as high as 218 kA/cm², spanning seven orders of magnitude, have been obtained ^{[4] [5]}. A resistive cut-off frequency of 20.2 GHz has been realized on photolithography defined SiGe RITD followed by wet etching for further reducing the diode size ^[5], which should be able to improve when even smaller RITDs are fabricated using techniques such as electron beam lithography.

Applications

In addition to the realization of integration with Si CMOS and SiGe HBT that is discussed in the next section, other applications of SiGe RITD have been demonstrated using breadboard circuits, including multi-state logic ^[6].

Integration with Si/SiGe CMOS and HBTs

Integration of Si/SiGe RITDs with Si CMOS has been demonstrated ^[7].

Vertical integration of Si/SiGe RITD and SiGe HBT was also demonstrated, realizing a 3-terminal negative differential resistance circuit element with adjustable peak-to-valley current ratio ^[8].

These results indicate that Si/SiGe RITDs is a promising candidate of being integrated with the Si integrated circuit technology.

References

1. ^ ^a  S.L. Rommel, T.E. Dillon, M.W. Dashiell, H. Feng, J. Kolodzey, P.R. Berger, P.E. Thompson, K.D. Hobart, R. Lake, A.C. Seabaugh, G. Klimeck, and D.K. Blanks, Room Temperature Operation of Epitaxially Grown Si/Si_0.5Ge_0.5/Si Resonant Interband Tunneling Diodes, Applied Physics Letters 73, 2191 (1998).
2. ^  S.-Y. Park, S.-Y. Chung, P.R. Berger, R. Yu, and P.E. Thompson, Low sidewall damage plasma etching using ICP-RIE with HBr chemistry of Si/SiGe resonant interband tunnel diodes, IEE Electronics Letters 42, 719 (2006).
3. ^  R. Duschl and K. Eberl, Physics and applications of Si/SiGe/Si resonant interband tunneling diodes, Thin Solid Films 380, 151 (2000).
4. ^  N. Jin, S.Y. Chung, R. Yu, R.M. Heyns, P.R. Berger, and P.E. Thompson, The effect of spacer thicknesses on Si-based resonant interband tunneling diode performance and their application to low-power tunneling diode SRAM circuits, IEEE Transactions on Electron Devices 53, 2243 (2006).
5. ^  S.Y. Chung, R. Yu, N. Jin, S.Y. Park, P.R. Berger, and P.E. Thompson, Si/SiGe Resonant Interband Tunnel Diode with f_r0 20.2 GHz and Peak Current Density 218 kA/cm² for K-band Mixed-Signal Applications, IEEE Electron Device Letters 27, 364 (2006).
6. ^  N. Jin, S.Y. Chung, R.M. Heyns, and P.R. Berger, R. Yu, P.E. Thompson, and S.L. Rommel, Tri-State Logic Using Vertically Integrated Si Resonant Interband Tunneling Diodes with Double NDR, IEEE Electron Device Letters 25, 646 (2004).
7. ^  S. Sudirgo, D.J. Pawlik, S.K. Kurinec, P.E. Thompson, J.W. Daulton, S.Y. Park, R. Yu, P.R. Berger, and S.L. Rommel, NMOS/SiGe Resonant Interband Tunneling Diode Static Random Access Memory, 64th Device Research Conference Conference Digest, page 265, June 26-28, 2006, The Pennsylvania State University, University Park, PA.
8. ^  S.Y. Chung, N. Jin, and P.R. Berger, R. Yu, P.E. Thompson, R. Lake, S.L. Rommel and S.K. Kurinec, 3-Terminal Si-Based Negative Differential Resistance Circuit Element with Adjustable Peak-To-Valley Current Ratios Using a Monolithic Vertical Integration, Applied Physics Letters 84, 2688-2690 (2004).

See also

• Si Esaki tunnel diode
• Resonant tunnel diode
• Resonant interband tunnel diode
• Si/SiGe resonant tunnel diode