Si/SiGe resonant interband tunnel diode

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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.

Contents

[edit] Background

Resonant interband tunnel diodes are different from another type of tunnel diodes, called resonant tunnel diode (RTD)s, which are actually resonant intraband tunnel diodes.

Resonant tunnel diodes are typically realized in III-V compound material systems, where hetrojunctions made up of various III-V compound semiconductors create quantum wells that enable resonant tunneling. Resonably 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.

There were efforts to make Si/SiGe resonant tunnel diode, but the perfomance was limited due to the limited conduction band and valence band discontinuities between Si and SiGe alloys. Resonant tunneling of holes through Si/SiGe heterojunctions was attempted first because of the typically relatively larger valence band discontinuity in Si/SiGe heterojunctions than the conduction band discontinuity. This has been observed, but negative differential resistance was only observed at low temperatures but not at room temperature [1]. Resonant tunneling of electrons through Si/SiGe heterojunctions was obtained later, with a limited peak-to-valley current ratio (PVCR) of 1.2 at room temperature [2]. Subsequent developments have realized Si/SiGe RTDs (electron tunneling) with a PVCR of 2.9 with a PCD of 4.3 kA/cm2 [3] and a PVCR of 2.43 with a PCD of 282 kA/cm² at room temperature [4].

Interband resonance tunnel diodes combines the structure and behavior of both resonant tunneling diodes and conventional tunnel diodes, and electronic transition occurs between the energy levels in the quantum wells in the conduction band and that in the valence band [5]. InAlAs/InGaAs RITDs with PCVRs higher than 70 [6] and as high as 144 [7] at room temperature and Sb-based RITDs with room temperature PVCR as high as 20 [8] have been obtained. But the main drawback of III-V RITDs is the use of III-V materials.

Si/SiGe resonant interband tunnel diodes are developed [9], which offer the advantage of being compatible with the mainstream Si CMOS technology.

[edit] Structure

Typical structure of a Si/SiGe resonant interband tunnel diode
Enlarge
Typical structure of a Si/SiGe resonant interband tunnel diode
Calculated band diagram of a typical Si/SiGe resonant interband tunnel diode
Enlarge
Calculated band diagram of a typical Si/SiGe resonant interband tunnel diode

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 [9].

[edit] 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 [check paper for better/more words], 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 PCVR up to 6.0 [10], and current densities spanning seven orders of magnitude, from as low as 20 mA/cm² [11] to as high as 218 kA/cm² [12].

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 [13], which should be able to improve when even smaller RITDs are fabricated using teachinques such as electron beam lithography.

[edit] 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 [14].

[edit] Integration with Si/SiGe CMOS and HBTs

Integration of Si/SiGe RITDs with Si CMOS has been demonstrated [15].

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 [16].

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

[edit] References

  1. ↑  U. Gennser, V.P. Kesan, S.S. Iyer, T.J. Bucelot, and E.S. Yang, J. Vac. Sci. Technol. B 8, 210 (1990)
  2. ↑  K. Ismail, B.S. Meyerson, and P.J. Wang, Electron resonant tunneling in Si/SiGe double barrier diodes, Appl. Phys. Lett. 59, 973 (1991)
  3. ↑  P. See, D.J. Paul, B. Hollander, S. Mantl, I. V. Zozoulenko, and K.-F. Berggren, High Performance Si/Si1 xGex Resonant Tunneling Diodes, IEEE Electron Device Letters 22, 182 (2001)
  4. ↑  P. See and D.J. Paul, The scaled performance of Si/Si1-xGexresonant tunneling diodes, IEEE Electron Device Letters 22, 582 (2001)
  5. ↑  M. Sweeny and J.M. Xu, Resonant interband tunnel diodes, Appl. Phys. Lett. 54, 546 (1989)
  6. ↑  D.J. Day, Y. Chung, C. Webb, J.N. Eckstein, J.M. Xu, and M. Sweeny, Double quantum well resonant tunnel diodes, Appl. Phys. Lett. 57, 1260 (1990)
  7. ↑  H.H. Tsai, Y.K. Su, H.H. Lin, R.L. Wang, and T.L. Lee, P-N double quantum well resonant interband tunneling diode with peak-to-valley current ratio of 144 at room temperature, IEEE Electron Device Letters 15, 357 (1994)
  8. ↑  J. R. Soderstrom, D. H. Chow, and T. C. McGill, New negative differential resistance device based on resonant interband tunneling, Applied Physics Letters 55, 1094 (1989)
  9. ↑ 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/Si0.5Ge0.5/Si Resonant Interband Tunneling Diodes, Applied Physics Letters 73, 2191 (1998)
  10. ↑  R. Duschl and K. Eberl, Physics and applications of Si/SiGe/Si resonant interband tunneling diodes, Thin Solid Films 380, 151 (2000)
  11. ↑  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)
  12. ↑  S.Y. Chung, R. Yu, N. Jin, S.Y. Park, P.R. Berger, and P.E. Thompson, Si/SiGe Resonant Interband Tunnel Diode with fr0 20.2 GHz and Peak Current Density 218 kA/cm² for K-band Mixed-Signal Applications, IEEE Electron Device Letters 27, 364 (2006)
  13. ↑  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)
  14. ↑  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
  15. ↑  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)

[edit] External links

[edit] See also

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