STORAGE CELL FOR A CHARGE TRANSFER BUCKET-BRIGADE CIRCUIT

1. A storage cell for a so-called bucket brigade device having a serially connected sequence of such cells, comprising a semiconductor substrate (102) of a first conductivity type with a source region (104') for a first cell, of a second conductivity type having a predetermined thickness, a drain region (104) for this cell, of the second conductivity type, spaced from the source region, having a first dopant concentration and a predeterminde thickness, also comprising a first ion-implanted drain region (107) for the first cell, of the second conductivity type having a second dopant concentration less than the first dopant concentration and a thickness less than the thickness of the source and the drain region, located between the drain region and the source region, spaced therefrom and immediately adjacent to the drain region, as well as with a thin insulating layer (110) lying on the surface of the substrate (2) over the channel and the first ionimplanted drain region (107), a thick insulating layer (106) lying on the surface of the substrate over the source and the drain region (104), and a gate electrode (112) lying over the thin insulating layer (110), characterized in that immediately adjacent to the first ion-implanted drain region (107) for the first cell, of the second conductivity type having a second dopant concentration, there is a second ion-implanted drain region (113) of the second conductivity type having a third dopant concentration less than the second dopant concentration, said second ion-implanted drain region being spaced from the first source region and having a thickness less than the first ionimplanted drain region, so that the resultant structure constitutes two combined FET elements with different threshold values, which as a combination of a charge storage capacitor with a field-effect transistor form a storage cell.