SEMICONDUCTOR DEVICES

Dopingless impact ionization MOS (DL-IMOS)——a remedy for complex process flow

Sangeeta Singh and P. N. Kondekar

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 Corresponding author: Sangeeta Singh, Email: sangeeta.singh@iiitdmj.ac.in

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Abstract: We propose a unique approach for realizing dopingless impact ionization MOS (DL-IMOS) based on the charge plasma concept as a remedy for complex process flow. It uses work-function engineering of electrodes to form charge plasma as surrogate doping. This charge plasma induces a uniform p-region in the source side and an n-region in the drain side on intrinsic silicon film with a thickness less than the intrinsic Debye length. DL-IMOS offers a simple fabrication process flow as it avoids the need of ion implantation, photo masking and complicated thermal budget via annealing devices. The lower thermal budget is required for DL-IMOS fabrication enables its fabrication on single crystal silicon-on-glass substrate realized by wafer scale epitaxial transfer. It is highly immune to process variations, doping control issues and random dopant fluctuations, while retaining the inherent advantages of conventional IMOS. To epitomize the fabrication process flow for the proposed device a virtual fabrication flow is also proposed here. Extensive device simulation of the major device performance metrics such as subthreshold slope, threshold voltage, drain induced current enhancement, and breakdown voltage have been done for a wide range of electrodes work-function. To evaluate the potential applications of the proposed device at circuit level, its mixed mode simulations are also carried out.

Key words: impact ionization MOSFET (IMOS)dopinglesswork-function engineeringDebye lengthdrain induced current enhancement (DICE)random dopant fluctuations (RDF)



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Fig. 1.  Schematic cross-sectional view of (a) conventional IMOS and (b) DL-IMOS.

Fig. 2.  (a) Charge plasma formation under impact of the work-function difference of the two metals (M$_{1}$ and M$_{2}$) electrodes. (b) Conduction mechanism in DL-IMOS.

Fig. 3.  (a) Conventional IMOS process flow. (b) TEOS based IMOS process flow[13]. (c) DL-IMOS proposed process flow. The advantages are no ion implantation, photo-masking and lithography is required for DL-IMOS.

Fig. 4.  Proposed process flow for the fabrication of DL-IMOS.

Fig. 5.  Electron and hole concentration of DL-IMOS and conventional IMOS along the device length with X-X' cut-line under (a) thermal equilibrium, (b) OFF state, (c) ON state, and energy band diagram for (d) thermal equilibrium, (e) OFF state, (f) ON state. Thermal equilibrium ($V_{\rm G}$ $=$ 0 V, $V_{\rm SD}$ $=$ 0 V), OFF state ($V_{\rm G}$ $=$ 0 V, $V_{\rm SD}$ $<$ 0 V and ON state ($V_{\rm G}$ $>$ 0 V, $V_{\rm SD}$ $<$ 0 V). This novel biasing scheme is reported in Reference [8].

Fig. 6.  (a) Transfer characteristics of DL-IMOS and the conventional IMOS. (b) Breakdown characteristics ($I_{\rm D}$-$V_{\rm DS}$) of DL-IMOS and the conventional IMOS, where $\phi _{\rm M1}$ is taken as 5.93 eV and $\phi _{\rm M2}$ as 3.9 eV.

Fig. 7.  (a) Electric field profile of DL-IMOS and the conventional IMOS and (b) impact ionization rate of DL-IMOS and the conventional IMOS, along the device length with X-X$'$ cut-line in On state.

Fig. 8.  (a) DICE and SS variation as a function of $(\phi_{\rm M1})$ and $\phi _{\rm M2}$ is fixed as 3.9 eV for DL-IMOS. (b) Threshold voltage $V_{\rm th}$ and breakdown voltage $V_{\rm Br}$ variation as a function of $(\phi_{\rm M1})$ and $\phi _{\rm M2}$ is fixed as 3.9 eV for DL-IMOS.

Fig. 9.  (a) DICE and SS variation as a function of $(\phi_{\rm M2})$ and $\phi _{\rm M1}$ is fixed as 5.93 eV for DL-IMOS. (b) Threshold voltage $V_{\rm th}$ and breakdown voltage $V_{\rm Br}$ variation as a function of $(\phi_{\rm M2})$ and $\phi _{\rm M1}$ is fixed as 5.9 eV for DL-IMOS.

Fig. 10.  (a) Schematics of resistive load inverters using DL-IMOS having a load resistor of 100 k$\Omega$. (b) Simulated voltage-transfer characteristics of resistive load inverters using DL-IMOS.

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Table 1.   Simulation parameters for conventional IMOS and DL-IMOS.

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Table 2.   Comparison of DL-IMOS fabrication flow with previous work.

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    Received: 01 January 2015 Revised: Online: Published: 01 July 2015

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      Sangeeta Singh, P. N. Kondekar. Dopingless impact ionization MOS (DL-IMOS)——a remedy for complex process flow[J]. Journal of Semiconductors, 2015, 36(7): 074001. doi: 10.1088/1674-4926/36/7/074001 S Singh, P. N. Kondekar. Dopingless impact ionization MOS (DL-IMOS)——a remedy for complex process flow[J]. J. Semicond., 2015, 36(7): 074001. doi: 10.1088/1674-4926/36/7/074001.Export: BibTex EndNote
      Citation:
      Sangeeta Singh, P. N. Kondekar. Dopingless impact ionization MOS (DL-IMOS)——a remedy for complex process flow[J]. Journal of Semiconductors, 2015, 36(7): 074001. doi: 10.1088/1674-4926/36/7/074001

      S Singh, P. N. Kondekar. Dopingless impact ionization MOS (DL-IMOS)——a remedy for complex process flow[J]. J. Semicond., 2015, 36(7): 074001. doi: 10.1088/1674-4926/36/7/074001.
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      Dopingless impact ionization MOS (DL-IMOS)——a remedy for complex process flow

      doi: 10.1088/1674-4926/36/7/074001
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      • Corresponding author: Email: sangeeta.singh@iiitdmj.ac.in
      • Received Date: 2015-01-01
      • Accepted Date: 2015-01-29
      • Published Date: 2015-01-25

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