Guard Ring Designs on Photovoltaic Energy Harvesting Silicon LSIs

This study explores strategies for safeguarding complementary metal–oxide–semiconductor (CMOS) field-effect-transistors (FETs) and PN-diode against bulk carrier contamination for energy harvesting applications. Energy harvesting processes can generate excessive carriers within the bulk region, which can penetrate the PMOS region from the p(P-Sub)/n(NWell) junction or <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nmosfet</small> without triple-well. To address this problem, this study investigated the effectiveness of a guard ring structure in protecting <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cmosfet</small>s and PN-diode by recombining carriers in their vicinities. The formation of unpassivated metals around <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cmosfet</small>s serves as a catalyst for carrier elimination before they penetrate the NWell region of a <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pmosfet</small> or the <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nmosfet</small> itself, thereby improving the <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> states of both FETs. For a PN diode, the smaller off-current and lower threshold voltage obtained are advantageous for low-power consumption. However, such guard ring also degrades the performance of a photovoltaic (PV) cell by recombining the carriers needed by the cell to generate power. The experimental study of PV cells w/back-surface-field (BSF) and w/o BSF revealed that the former reduced the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$V_{\text{OC}}$</tex-math></inline-formula> of the cell with and that caution is required when forming a guard ring nearby the PV cell.