High k dielectrics


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High k dielectrics

  1. 1. A Seminar on HIGH-K DEVICES Name: Subash John Roll number: CGB0911005 Course: M.Sc. [Engg.] VLSI System Design Module Code: VSD527 Module Title: Integrated Circuit Analysis and Design Module Leader: Prof. Cyril Prasanna Raj P.24/10/2011 1 M.S.Ramaiah School of Advanced Studies, Bangalore
  2. 2. Contents• Introduction• Problem with SiO2• What is high-k?• Why high-k dielectric?• High-k and polysilicon interface• Use of metal gates• The high-k – metal gate solution• Future scope• References 2 M.S.Ramaiah School of Advanced Studies, Bangalore
  3. 3. Introduction• Since the 1960‟s semiconductor industry has used poly-Silicon gate with a Silicon dioxide gate dielectric layer.• As transistor sizes are shrinking, the gate dielectric and Silicon dioxide are only a few atomic layers thick.• Further scaling would increase the already-problematic gate current leakage (IG) and lead to power loss, increased power consumption, and generate excess heat.• Intel has achieved a significant breakthrough in transistor technology by developing high-k + metal gate transistors for its 45 nm node codenamed Penryn processor that significantly reduces leakage power, deliver higher performance and greater energy efficiency• Use of HfO2 (k=20), ZrO2 (23), and Ta2O5 (26) as high-k gate-dielectrics. 3 M.S.Ramaiah School of Advanced Studies, Bangalore
  4. 4. Problem with SiO2• SiO2 layer thickness has shrunk to 1.2nm (5 atoms) for 90nm node• Due to excessive tunneling current, it would stop playing role of an insulator C• The capacitance of the gate can be modeled as a parallel-plate capacitor• Since the t is greater for the new dielectric gate material, it requires an even larger dielectric constant k to increase the overall capacitance – that‟s where the new high-k dielectric materials come into play. Figure 1 Oxide thickness vs. Gate leakage 4 M.S.Ramaiah School of Advanced Studies, Bangalore
  5. 5. What is High-K?• The dielectric constant, k, is a parameter defining ability of material to store energy/charge.• “AIR” is the reference with “K=1”.• Silicon dioxide has k=3.9. Dielectrics featuring k>3.9 are referred to as “high”-k dielectrics.• A higher k value means a greater capacitance at greater thicknesses. Figure 2 SiO2 vs. HK 5 M.S.Ramaiah School of Advanced Studies, Bangalore
  6. 6. Why High-k dielectric?Figure 3 Capacitance vs. Dielectric thickness plot Figure 4 Leakage current vs. Vg plot 6 M.S.Ramaiah School of Advanced Studies, Bangalore
  7. 7. High-K and PolySilicon Interface Figure 5 HK and PolySi interface 7M.S.Ramaiah School of Advanced Studies, Bangalore
  8. 8. Mobility degradation and Phonon scattering at High-kPolySilicon interfaceFigure 6 Mobility vs. Electric field Figure 7 Phonon scattering 8 M.S.Ramaiah School of Advanced Studies, Bangalore
  9. 9. When SiO2 is replaced with a high-k material it was found that PolySi and High-k materialwere not compatible so PolySi is being replaced by a Metal to make it compatible with the high-k material. Figure 8 Conventional vs. HK based transistor 9 M.S.Ramaiah School of Advanced Studies, Bangalore
  10. 10. Use of Metal Gates• As a conductor, metal can pack in hundreds of times more electrons than poly silicon• Metal gate electrodes (Co, Ni, Mo, W) are able to decrease phonon scatterings and reduce the mobility degradation problem.• The key property - Work Function of metal. Figure 9 Scattering in Poly vs. Metal gate 10 M.S.Ramaiah School of Advanced Studies, Bangalore
  11. 11. Metal Gate• Metal gate screens surface phonon scattering and improves channel mobility in high-k transistors• Furthermore, a thicker Hafnium-based dielectric gate with a metal gate increases resistance and reduces the unwanted gate leakage current. Figure 10 Surface mobility vs. Electric field plot 11 M.S.Ramaiah School of Advanced Studies, Bangalore
  12. 12. The High-k – Metal gate solution Figure 11 HK + Metal gate solution 12M.S.Ramaiah School of Advanced Studies, Bangalore
  13. 13. The High-k – Metal gate solutionMetal Gate• Increases the gate field effectHigh-k Dielectric• Increases the gate field effect• Allows use of thicker dielectric layer to reduce gate leakage Figure 12 Gate leakage vs. Vgs plotHK + MG Combined• Drive current increased >20% (>20% higher performance)• Or source-drain leakage reduced >5x• Gate oxide leakage reduced >10x Figure 13 E-field vs. Technology node plot 13 M.S.Ramaiah School of Advanced Studies, Bangalore
  14. 14. Future scope• High-k dielectrics are vital for next-generation low power-consumption, low leakage, high performance logic devices• Formation and compatibility of high-k dielectrics better with non-silicon materials (non SiO2- based). Use of Germanium substrate with a high-k dielectric and a metal gate increases the total capacitance. 14 M.S.Ramaiah School of Advanced Studies, Bangalore
  15. 15. References[1] Chao, L. (2008) „Intel‟s 45nm CMOS Technology‟ Intel Technology Journal [online] 12(3). available from <http://www.intel.com/technology/itj/2008/v12i2/index.htm> [23 Oct 2011][2] Intel 45nm high-k metal gate press release (2007), Intel Demonstrates High-k + Metal Gate Transistor Breakthrough on 45nm Microprocessor [online] available from <http://www.intel.com/pressroom/kits/45nm> [21 Oct 2011][3] Mark T. Bohr (2007), The High-k Solution [online] available from <http://spectrum.ieee.org/semiconductors/design/the-highk-solution> [16 Oct 2011] 15 M.S.Ramaiah School of Advanced Studies, Bangalore
  16. 16. THANK YOU 16M.S.Ramaiah School of Advanced Studies, Bangalore